You might have a little easier time finding a class C that meets your parameters.
It's often a little (not necessarily a lot) easier and less expensive to keep a class C running reliably because there are more shared parts with common vehicles. It may also be a little easier to find shops that will work on them for this reason. Tires are often a good bit cheaper; a set of six decent 16" tires for a class C can be had for around $1000.
In any case, look for no signs of water damage, but evidence of ongoing roof maintenance (particularly for rubber and TPO roofs). Look for reasonably fresh tires (or budget for replacements). Give some thought to how you'd find the space for living: is there sufficient storage in the kitchen for the wares you'd need? Is the counter space large enough to open a can without putting a cover over the sink? Can you turn around in the shower or (if you're somewhat tall) take a shower without having to hunch over?
Do be aware that ongoing maintenance on any RV, particularly an older one, is going to involve some continuing expenses. There are many fiddly bits and parts that like to break down or wear out.