When I bought my Medic Master/Freightliner, it had been refurbished for sale to an ambulance company. Because I was a private party, the exterior lights were changed to white or yellow lenses, the siren amplifier was removed, and any reference to "ambulance" on the outside was removed. This was carefully done, and all I'll have to do is a little buffing to remove the last vestiges of ambulance lettering. I traded the cot hardware and the oxygen gear to the dealer (plus some cash) for new front tires. The price included 4 new group 31 batteries, a new Vanner inverter, a new 270 amp alternator, a new air compressor, plus changing all the fluids and filters, and a complete lube job. The dealer road tested it, and anything needing service was serviced. When I bought it, we took it for a road test with a punch list to check for anything that needed repair - there was nothing.
Thankfully, I have conventional relays instead of a digital system. I can buy a new Bosch relay for $4, versus going to Weldon for a VMUX component.
I like a larger truck with decent towing capabilities (a 5.9 engine also helps), and my garage can swallow a medium ambulance (with a little sorting). I have headroom and elbow room, plus a rig that's fun to drive. My son and I drove it from PA back to MSP after I picked it up - 70 MPH all the way.
I paid a little more - but I got a lot more than buying a worn out ambulance - it had only 51,000 miles on the clock when I bought it.
If you're looking at used ambulances, look and think before you leap - don't only use price as your guide.