Have you checked the area you want to be in for parks?
Some RV parks can/will refuse a rig over 10 years old. So find a place you might like first for their rules.
For 12K for the first Class C you will be looking at older used.
Any rig with tires over 6-7 years will need new tires if you plan to do any traveling. Forget how they look. They can look brand new and have only a couple hundred miles on them but they are still NO GOOD.
RV fridge in an older unit may be on the way out but if you plan to stay in one place it can be changed to a regular household fridge.
I think in our situation it is an unwise move but it is your move
your expenses will be;
Lot rent
Electric
propane .
maybe taxes
Will the park you are in allow propane to be delivered or will you have to drive the rig to get propane.
Can you fix the problems on the rig yourself or will you have to pay when the furnace fails etc
Lastly do you have enough knowledge to buy an older rig without getting taken and having a rig that is a disaster (there can be a lot of hidden damage) and no money for repairs. Lots of first time buyers get taken on older units. What would you do then?