I've never sold a business, but came close to buying a couple.
There will be local business brokers that you could reach out to-they may have some free advice on valuation. If you list it with them their cut will be significant.
A shop like that would usually be valued at 2x owner benefit. Owner benefit can be defined a bunch of ways, but unless your uncle is making 100k per year, or the tooling is worth a bunch of money, the 200k figure will be tough to hit. Other things that can, but probably won't factor into the price is name recognition, intellectual property, the customer list, the value of a under-market lease, etc.
Good Luck!