Paid $2K for our Class C in April 2006. Put less than 1K into it. Motor/tranny was all sound. Just replaced 2 tires recently but we don't count that. Have the same old stove, AC unit and furnace. Kept the old cabinet face frames and rebuilt the carcasses (boxes). Replaced old RV fridge with 110vAC mini fridge and mini freezer. Replaced old countertop. No flooring in yet but it will be wood parquet (cheap) so I'm on plywood subfloor... need to add a layer of foamboard insulation underneath... the floor got awfully chilly this past winter. New interior wall covering and ceiling covering. Rebuilt part of cabover section (rotted). Rebuilt part of roof (rotted) Patched and resealed exterior roof. Working on patching up exterior skin so I can repaint with a 25 ft paint job (looks okay from 25 ft away

). Need to install my freshwater tank (have it just not installed it) and rework the plumbing so we can fill the tank thru the city water connection.
You can spend a fortune rehabing these units. You need to decide how far you want to upgrade and how much you want to spend. Make a list of must do, and want to then a "if we have enough $$ we can..." For us, this is a short term situation (I hope). We have a bus to convert and the Class C is a test subject for many things. One of which is how little (or how much) space we need for some things. I have discovered we need 18" hanging space per person for 8 days worth of clothing. This is much less than I had originally thought. I need more (and better laid out) food/appliance storage space. I NEED a dishwasher... I hate washing dishes. AN ISLAND BED, I'm getting too old to be crawling over someone to get in/out of bed. These are just a few things. Oh, and I need more space to carry more books with me (David will disagree but I really do... books are right up there with oxygen). Get the roof fixed first (it most likely leaks), get the rot out (from the old leaks) and make sure the thing is in running order... You should be able to drive it down the road before you start in the interior stuff. Make sure you check around the windows and doors (even down on the floor) and under the sink/bathroom for rotted areas. Now, go rent "The Money Pit" and be thankful that your RV is small.

The tool to recrimp the pipes is pricey. We have two... one does two pipe sizes and cost us $200 and the one that only does one size pipe cost $100. Make sure that pipe doesn't have a crack in it when you repair. Otherwise you will make the repair and still have the same leak.
And no matter how much money you sink into the RV, YOU WILL NEVER GET THAT MONEY BACK! It's a proven fact, deal with it. That's not why we have all rehabbed older RV's. It usually involves not having RV payments and getting an RV that suits us.