I got quoted ~$900 to replace the lower motor & trans mount for my GP.

[Explicit_Spade]

this might be the worst case of shady mechanics I've heard of. I would go on that dudes page and give him a horrible rating.

I disagree with this. How many hours of labor is it quoted at and what is their parts cost?

Remember that shops have certain parts stores they deal with and a certain markup on those parts. If their price for parts was $120, and it's quoted as a 9 hour job at $80/hour that's $840 total.

Shops don't charge actual labor time, they charge quoted labor time, so even if it takes them an hour, and the time on the books is 10 hours, you will pay for the 10 hours. That's just how it works.