Excellent write-up, I would have loved to have seen it 8mos ago before I learned so much more about ambo's than I expected to--but it was too much fun researching!
(keep in mind many of the links below may not work. I'm just copying/pasting a lot of info from the huge ambo document I compiled during my research)
If we're talking '97+ ambo's, $3000-6500 will probably net you one with higher mileage, or rusty. Not saying these deals aren't out there, but for a super clean one that's been well maintained, you'll probably be spending more money...at least from my research 8mos ago--but again I was looking for a '00+ 7.3L-TD or 6.0L-TD. $8000 was the lowest priced 7.3L-TD 138"WB Type3 MiniModule I found. There were 4 of those to choose from, all with 300k+.
Most Type3 Mini-Mod's(ie mini module) were 64/66/68" interior height until about 2010(due to the KKK ambo regulations/standards(although the coach builder could have made it on a custom order per Jason at VCI)), when most became 72". So if you're 6' like myself, the 64-68" interior height might be a bit uncomfortable.
Most Type3 Mini-Mod's I found were 138"WB and 145" module length. Non-Mini-Mod's were 158"--be aware of that break over angle if you won't be going to 4WD soon.
Module lengths are typically 164"-170". Overall length is usually 252"-270"(but some don't include the bumpers so this figure could be off depending on their measuring method).
Shortest Type3 M-M w/ 138"WB I've seen is 248" overall, most of the Typ3 Std-M's w/ 158"WB I found are 270" overall.
Most 4WD Type3 ambo's were done by Quigley. I must say I love my UJOR setup instead!!
Type1 ambo's like a Ford F350/450 could come as factory 4x4 from Ford, saving you the money of a 4WD conversion. The trick with these Type1's is finding a walk-thru module, as most don't seem to be. Most Type3's are walk-thru's.
Big advantage to Type1 and 3's are the flat vertical(square) walls, vs angled-in walls of the Type2 van.
Seems that most Type1 and 3's were Ford, some Chevy. Most Type2's Ford, some newer ones Sprinter's.
Big issue with a SRW(single rear wheel) is offroad tire choices due to load rating. All depending on what size you're going to go with, you may have trouble finding a tire with a high enough load rating. This is why the Toyo M/T's are popular--because they have sufficient load rating for the heavier rigs.
From my research and talking to lots in the industry, thoughts on ambo coach builders/brands;
From Steve Apgar; As far as the best Module, I have sold every brand of new and used in the 800 plus units I have moved. I worked for Wheeled Coach, Medtec, Braun of Ohio, Medix and Demers. I feel like Demers, Lifeline, Horton, Wheeled Coach, and Medix have given me fewest headaches on build quality. I think older Hortons, McCoy Millers are sometimes problematic electrical systems. The remount experts tend to prefer Wheeled Coach for remounting due mostly to how solid the electrical system is to re attach.
-Wheeled Coach from FL;
http://arrowmfginc.com/listing/truck/49030/
http://www.commercialtrucktrader.com/listing/2006-FORD-E350-XLT-110477840
http://www.commercialtrucktrader.com/listing/2006-FORD-F450-110860947
-Horton;
http://www.lifestarrescue.com/used-...41/2003-ford-e-450-horton-type-3-unit-lsr-824
http://www.firetrader.com/viewad.asp?id=50286546714100719
http://vciambulances.com/vehicle-sales/ambulances/horton#History
http://vciambulances.com/vehicle-sales/ambulances/horton/type-iii/model-453
http://vciambulances.com/Portals/0/Ambulances/Horton/Type III/453/VCI-Horton-Type-III-Model-453-Ford-drawings.pdf
403 is 137” box, 64” headroom
453 ‘10+ is 145” box, 72” headroom. Would want Wall Cabinet B, no CPR seat.
Horton made a 523 in '97-03 which was a 157” box
533 is 163” box
403/453 on 138”WB, 523/533 on 158”WB—difference in length is behind rear axle so a 533 add 6” to rear of box
-Medix;
http://www.commercialtrucktrader.com/listing/2006-FORD-F-350-SUPER-DUTY-AMBULANCE-PACKAGE-111212646
http://www.globalemergencyvehicles....Type-III-Medix-Refurbished-Ambulance-For-Sale
-Demers
-Lifeline
-Road Rescue;
http://www.firetrader.com/viewad.asp?id=50286991165100719
http://arrowmfginc.com/listing/truck/14900/
-AEV;
http://ambulancetrader.com/adDetails.cfm?aid=2139&cat=Type III
http://www.fentonfire.com/ambulances/listing.php?lid=5990
CitiMedic Plus (Typ3 MiniMod);
http://www.wheeledcoach.com/products.htm?productTypeID=2&productID=15
-Osage; some of the nicest finishes, stainless panels. Jason at VCI says they're lower quality behind panels/etc
http://arrowmfginc.com/listing/truck/47595/
-Medtec; (Medtec now bought out by someone else)
http://arrowmfginc.com/listing/truck/48718/
-McCoy Miller; Jason at VCI says they're lower quality behind panels/etc
http://www.adirondackfire.com/2001 Ford-Mccoy Miller1.htm
http://ambulancetrader.com/adDetails.cfm?aid=3761&cat=Type III&thisImg=DSC05456.JPG
-Braun
Best sites to search for an ambo(in order)--yes, many of these will be hugely expensive as they're targeted to municipalities with bigger budgets;
http://arrowmfgtrucks.com/
http://arrowmfginc.com/for-sale/
http://vciambulances.com/vehicle-sales/preowned-used-ambulances
http://www.globalemergencyvehicles.com/units-in-stock/ambulance-for-sale
http://ambulancetrader.com/
http://www.ambulancemarket.com/used-ambulances-for-sale/4-type-iii.html
http://www.commercialtrucktrader.com/Ambulance-For-Sale/search-results?category=Ambulance|2000545
http://www.govdeals.com
http://www.governmentfiretrucks.com
http://www.lifestarrescue.com/used-ambulances
http://www.firetruckmall.com/AvailableTrucks/Rescue-Trucks-Squads.aspx
http://www.firetec.com/category/Ambulance.html
http://www.fentonfire.com/ambulances/
http://www.firetrucksunlimited.com/used-fire-trucks-for-sale/
http://www.proambulance.net/available-units
http://peachstateambulance.com/category/products/pre-owned/
http://www.heartlandwheels.com/Ambulance/Used_Amb.htm (most look fairly beat)
http://www.fescosales.com/usedveh.asp
http://www.emergencyvehiclecenter.com/Pages/used_stock.htm
http://www.ambulancesales.net/ (tons of MiniMods, although most look fairly beat)
http://stateambulance.com/Home.aspx
Cab/chassis;
http://www.truckpaper.com
http://www.commercialtrucktrader.com/Ford-E350-Cab-Chassis-For-Sale/search-results?category=Cab+Chassis|2000881&make=FORD|2310392&model=E350|764865589&page=1
Remounts/(modifications?);
http://arrowmfginc.com/ambulance-remounting/
http://www.proambulance.net/remount-services
http://vciambulances.com/remounts
http://fireserviceinc.com/
http://peachstateambulance.com/
Cabin/module builders(for ideas);
-Unicat;
http://www.unicat.com/ua-en/
-Earthroamer;
http://earthroamer.com/
-Global Expedition Vehicles;
http://globalxvehicles.com/vehicles/
-Tom's;
http://www.toms-fahrzeugtechnik.com/
-XP Camper;
http://xpcamper.com/
-Uro-Camper;
http://www.uro-camper.com/web/en/
Why did I go with an E350 RB vs an ambo? After much deliberation, I was a bit concerned with an 8' wide module, for tighter trails. Would I have been able to take a Type3(after a UJOR conversion) on the White Rim Trail in UT? No, I would have been too wide for some areas of the trail. Thankfully I had VANdiana to get me thru.
For open terrain where there aren't tighter trails, an ambo sure if one heck of a stout rig for the money!
I hope this info helps.