91/30's still online from $120-$150 at numerous suppliers, Buds includes shipping in that price.
Been discussed before, surplus will "dry-up" to some extent, exactly how much is unknown- as is the number of MN's still stacked up in underground armories in Russia. Remember, there were 18,000,000 of them made- that's a lot of rifles...
Natch, many are no longer in circulation, but there's no way to know whether the supply has really been greatly diminished, or if they're just "allocating" to keep prices up.
The 7.62 x 54R is still a round in active military use (PKM machine gun and PSL) in a number of countries- so the ammo is still being made, but of course not as much as was 30 or 40 years ago.
Far as bang for your buck, depends on what you do with it...Surplus is OK for "plinking", but wholly inaccurate for any kind of shooting that demands serious accuracy- which is why I've never put a single round of surplus through my MN's- only SMK handloads.
It can be economical as a hunting rifle though- with SP factory ammo at about $.50 round it's better than most, and the round will take anything in North America.