My guess is total cost would be around $1,600.
You'll need a new barrel that can accept the suppressor - $250
Decent Suppressor - $800
Trust - $350
Stamp - $200
NICS - $5
Might be less for a .22. I never saw the point of a suppressed .22, though. I think suppressors are cool. But, it's just enough money and hassle for me to still not have one. I did the drill to get my one machinegun. PITA. That was enough for me.
My LGS offers the trust for free, and doesn't charge for the NICS check (you don't call it in on an NFA item anyway; you just fill out the 4473). Otherwise those numbers are about right for a good .45 can. A good .22 can would run about $400.