IMHO

"no rust and paint bright"
Mechanicals are fixable / replaceable. Rust = cancer = expensive at best vs a no win scenario.

"Vibration in the front end" Bad tire to any one of the many suspension links. Take it to a couple of very good alignment shops for an estimates.

$1200 for pipe and muffler after CAT is outrageous. I can't imagine it being anymore than a half hour job at any good muffler shop.

$2000 for head gasket & grind valves. "Grind valves" sounds like the shop is wasting your money. When doing a head gasket, it's realistic to also do water pump, front engine seal, serpentine belt and tensioner. In my area about $1500.

CASH is KING now with current financial crisis! Shop around, the repair shops are suffering and some are willing to discount to keep their cash flowing. If it's a small independent shop, put real "cash" on the table. He won't have to pay out the bank card fee, so it's more money for him.