The price can vary a great deal. I have experience with Gemtech, Jet,
awc, and SSK inustries products. Check out their websites, and pricing is usually available.
Just a note. Although it is possible, it is a heck of alot easier to suppress a slow cartridge, and I don't belive your 6mm falls into that category. I know this hurts some of the long range attributes, but it is something to think about.
"It is not the critic who counts, not the man who points out how the strong man stumbled, or where the doer of deeds could have done better. The credit belongs to the man who is actually in the arena, who's face is marred by dust and sweat and blood, who, at the worst, if he fails, at least fails while daring greatly, so his place shall never be with those cold and timid souls who know neither victory nor defeat."