Having just gone through this, I will give my input on what I did. I was having this very same conversation with myself - I even emailed Ujoint a few pretty sweet full-on 2wd conversion vans ads to look at, all decked out with captains chairs and leather. Most of them were E150's though.
But I quickly realized that looking for a E2/350 with a diesel and extended body that was ALSO already a cargo OR passenger van was very limiting. I found the price range was MOSTLY dictated by the engine, not the style of van. If it was a diesel, it was $$.
I recommend making a list of MUST haves. I HAD to have a diesel, I wasn't going to settle for anything else. I wanted a Factory turbo diesel, so that framed my search of years on the low end. Beyond that, I wanted an extended body for the type of travel I wanted to do.
The mileage was of little concern to me, but I wanted less than 200k miles on the motor. I knew I would be converting to 4 wheel drive, so any mileage on the tranny, axles and suspension was irrelevant as these would all be new/rebuilt anyhow.
As a last 'must', I established a price limit. I had an upper limit of $8k. This really boxed in my upper year range.
I now had a window of 1994ish to 2004ish (in my area, for that price range), turbo diesel and extended body. Naturally, this meant I could find a decked out early van, or a stripped down, high mileage newer cargo van. Either way, I was going to have a lot of interior work cut out for me.
Lastly, I would make your search area as BROAD as possible. Use something like
www.searchtempest.com to make your search area much more broad and all encompasing than just craigslist. I found my van in Albequerque and I'm in Denver. But a quick look at one way airfare and I could get a direct flight on Southwest for $50!! Add a cab ride and the fuel to get home and its under $200 and a 7 hour drive (what better time to find out the quirks of your new van?)
In the Denver market, I could easily double the money I paid for my van and sell it in one day simply because I got such a good deal on it, and there are hardly ANY diesel vans available. I figured even if I didn't fall in love with it, I could at least turn a quick profit.
Something that ALMOST made my list of MUST haves was a hightop/travel top. I knew I wanted the headroom, but it wasn't going to be a deal breaker. I have found traveltops in junkyards and on craigslist, so I figured I could add one later.
Hope that helps!