Advice on sheetrock and wall construction

[sixfour]

I, with the help of contractors, am turning a 300 sq ft garage/shop into a music teaching studio. I'd also like to do some recording in there and want it as quiet as possible. And our situation in the pandemic has made cost more of an issue.

The insulation has been done and it wasn't exactly ideal. I was hoping for roxul or something similar, but because of the wall thicknesses and R values needed, the ceiling is closed cell spray foam, and the walls are 3 inches of closed cell and 2 inches of open cell spray foam. So now I really want to get the drywall done in a way that will help with sound isolation, hopefully without enlarging our budget too much. Here is what I'm told are my options:

Regular ol' sheetrock and taping: $4000
Quietrock w/ sound caulk and putty: $4800 more
Hat channel and isolation clips: $8400 more

So I guess I'm wondering what is the best bang for my buck is. I don't think we can afford both the isolation clips and quietrock. I've read that the clips are very hard to install and if it's not done perfectly, it's a waste of money and effort. It seems like quietrock is relatively simple to install.

Another option I'm wondering about, but was not given, is two layers of drywall with green glue in between. I'm guessing, though, that it would be about the same price and effectiveness as quietrock.

I've done some drywall construction myself (interior wall construction) and am wondering how hard it would be for me to add the second layer of drywall and green glue myself. Or is that definitely biting off more than I can chew?

Any other options I should ask about? And FYI, this contractor is great at building houses, but he's not a studio builder or acoustician.

[DanDan]

Would it be possible to make wooden or steel framing isolated from the walls? That, an air gap damped with fibre, two layers of regular sheetrock, probably best bang per buck and better soundproofing.