You can get decent used class C's in that general price range. Do reserve some budget for inspections and repairs and general maintenance before setting out on long trip(s).
One possible source, that isn't great for everyone but works very nicely for many, is an ex-rental RV from e.g. CruiseAmerica. They do a good job of checking them over and reconditioning them before selling them. Note that rental RVs tend to be strongly built but somewhat austerely furnished, as makes sense for hard use by inexperienced people.
Probably the most important consideration for any used RV is the condition and quality of maintenance that has been done by the previous owners. Water leaks, in particular, can sometimes cause serious and expensive structural damage without appearing to be too bad at an initial glance. Having someone experienced inspect things is a good idea if you're not sure of your ability to do so properly (and quite possibly even if you are). Also verifying the operation of all the systems and appliances is wise, and of course checking the chassis over mechanically.
I bought my class C from a private seller who advertised it on Craigslist. Not all posters on Craigslist are honest (but not all are out to scam you, either).
Before jumping in, I would strongly suggest making a trip with a rental RV. You may find that, in practice, it's not quite what you were thinking it would be, and save yourselves a lot of money and grief. You also will get a better idea of some things to look for or not look for in an RV, and what features might be important to you.