M-2, the 91-30 with hex receiver is considered a replacement for the "Dragoon" model M-91, and is fine for GAF, as well as the original M-91 long rifle. For GAF match use, a proper size cast bullet with 10-12 grains of Trail Boss should work fine. I say proper size, because bore dimensions can vary some. I haven't worked much on jacketed loads for them(yet), but starting loads from the manuals should be ok. Also, look on the Hodgeon website for instructions for downloading H4895, they have done research on loading as low as 60% of max loads with it, and still performing well. But that's only H4895, NOT IMR4895.
Can't help on current prices, I've got 2 M-91 long rifles(Remington and New England Westinghouse) that were about $125 and 200,but that was yeaaaaarrrsss ago.