King huge, stop and take a breath here......
Yes tire company is ripping you off. Btw, etrailer.com has the best tire and parts prices for trailers I've found. If it cost more than hour car to mount and balance tell the shop to fo.
You winterized it, so does everything work? You towed it home, do the brakes work?
Guess before I opened my wallet to someone, even if I didn't know w t f I was doing, I'd fire everything up and see if it all works. Chances are you don't need to do much or anything if it's cherry like you said.
Congrats on the trailer, spend some time getting to know it! Plus you'll be moe knowledgeable if/ when you take it in.