I have brakes on all of my larger smokeless muzzleloader s and a few rifles due to heavy bullets and charges. (Up to a 350gr bullet over 152.5gr of imr4350 at around 3200 fps). While I have never paid for installation, I would assume the cost would be around $100 to $150 plus the brake. I thread, install, bore, profile, and finish all of my installations as I use Harrell's brakes. Most of mine are radials as I do little prone shooting. Tactical brakes are more effective but only by a slight margin and your neighbor at the range will hate you when you start blowing items off their bench.
One of the main reasons that I use brakes that must be finished is because prefinished brakes are overbored which reduces effectiveness. Also, you could end up with the bullet closer to one side than the other which will effect accuracy. Or, even worse, the bullet makes contact with the brake. This is why I would never use a clamp on brake.
Don't forget hearing protection when hunting with a brake. If you do, you will never forget again.