Cheap?? Don't you watch Judge Millian? She says "Buy cheap, buy twice". Probably been pre-owned by at least two previous owners and probably has had the benefit of lots of DIY repairs. If you aren't getting AC power through the shore power cable, and you are lucky, there may be a circuit breaker that just needs resetting. There should be a power panel somewhere inside that has circuit breakers for 110 volt AC and fuses for 12 volt DC power.
We made the same mistake as you and bought an old Class C from a nice elderly widow whose son and the next door neighbor had been doing DIY repairs on for years. The roof leaked and there was mold. The external body seams were leaking and had been resealed with silicone (wrong). Generator leaked gasoline and needed complete electrical overhaul ($800), the tires looked good but were old with sidewall cracks and came apart on the road , the flailing steel belt of a rear dual cracked the holding tanks and ripped through wiring. The water heater was shot, and the fridge worked but was antique looking and gross. The engine cooling system needed new clutch fan, radiator, water pump and all belts and hoses. The after market dash AC compressor and idler pulleys did not line up and chewed up belts. One of the old flexible brake lines ruptured internally causing sudden pull to the left nearly pitching us over a cliff near Big Sur.
We bought the nice looking, but worn out old RV for $13K and spent another $8K on it in new tires, repairs and replacements the first year just to make the old beater usable for touring and camping. We did finally get some use out of the rig but would have been much better off saving our money and buying a much newer rig. We should have known better, but we were young and knew nothing about RV's and bought on impulse. There are generic books at Camping World that show basic RV 12 volt DC and 110 volt AC wiring and electrical systems plumbing, and maintenance procedures. There are a lot of You Tube videos that show how to troubleshoot problems and replace things.
If you bought the rig really cheap, you might be better off to sell your rig before you start spending some $8K-$10K more on repairs to make it safe, reliable and comfortable to use for touring and camping. Don't drive on old tires that look new but have sidewall cracks and come apart on the road 500 miles from home. Flailing steel belts can damage holding tanks, wiring and propane lines, you can lose control. Old brake fluid and brake problems can cause loss of control on curvy downhill grades. Engine cooling system problems can cause breakdowns on the road. House battery and converter charger problems can be a real problem when lights, furnace and electronic appliance controls don't get needed 12 volt DC power.
Good luck with whatever you do.
