I totally emphasize with the difficulty of deciding, since I've been all over the map from mid 2000's minivans with fold down seats (examples on YT videos) to the "standard" cargo vans, Astro vans, conversion vans, class B's, passenger vans... It certainly can be overwhelming. If you watch YT videos on vandwelling, you'll notice many of the vans are older, not shiny new ones.
Combine 2 of the above posters input, go to a mechanic with any possibility (or find a seasoned person or mobile mechanic inspector) and set a price point that also has built in at least 1/3rd of the van cost for repairs down the road, (more than 1/3rd if it is less than $4K to buy).
Decide if you want windows (with the associated covering issues) or a "box" without windows (cargo with nothing) or in-between (cargo with both back and the side 60/40 door windows present).
Decide if you want to stoop/crawl around (low top van)or want the increased 10-12" height found in a mid-top (tv top) conversion van. You'll likely not find a cargo van with an extended roof without an extended hunt and a lot of luck.
Once you have a price point and have made the window decision, you've narrowed it down substantially. Then haunt Reddit and Craigslist ads for a week or more, no matter what the location (check the CL surrounding areas boxes or try a different city not too far off). Get a feel for prices.
Check on our "trading Post" subforum, occasionally members resell their vans (TxtoSturgis had one recently).
You can also send out an appeal to forum members to "bird-dog" for you with parameters given, so it's not a waste of their time.
Hope that helps.