I got a lot of my Nagants years ago when they were cheaper. I think my 91/30 was $40, my M44 was $80, my Valmet M39 was $175 and my 91/30 PU sniper (a real one) was $500. Now just last year I got lucky and found a sweet deal on an M38 for $125. I guess the dealer didn't keep track of what the prices were doing. I kept them all in original condition and figure that the price on them will only go up over the years.
As far as modifying them, if you do put a recoil pad on it, I guess that's alright, even though the recoil on these rifles, even the carbines, is way over-rated and not nearly as bad as some folks claim. I tend to think that many of the complaints about recoil come from a lot of folks that are used to 5.56 and 7.62X39 rounds that do have a lot less recoil but really, the 7.62X54R round isn't as bad as many make it out to be. But if you do put a puss-pad...uh, I mean recoil pad on the rifle, make sure it's something you can put back to original condition if you ever want to sell it later on. Like I said, originals kept as a piece of history tend to increase in value over the years when the supply dries up. However, put one piece on that rifle that's not correct and I won't touch it, no matter how much the Bubba job cost you or if I do, the price I will offer you will probably be pretty insulting.