The SVT-40 is one of the most fun for cheap guns you can get.
Spare mags are a pain to get but Westrifles got them for $55 at the moment which is a steal.
The SKS is easily my favourite rifle, good bang, great cost and quite a bit more controllable for us smaller framed people. Great for letting someone who hasn't done any shooting pop a couple off as the recoil is rather light and the rifle itself is a nice short carbine. There are so many after-market stocks and accessories for the SKS it isn't even funny which is nice because, aside from scopes and mounts the SVT's options for customization are pretty limited.
The 7.62x54r of the SVT and Mosin can punch holes through 1/4" and 1/2" steel plate no problem. Really not a great idea to stand anywhere near someone who's firing the SVT thanks to that muzzle brake. That muzzle blast'll scare the sh*t out of anyone who's not ready for it.
The 7.62x39mm does the 1/4" no problem but struggles a bit with the 1/2" using the standard surplus fmj rounds.
I don't have any experience with the Mosin Nagant but, at the price they go for it won't be long until I call one my own.
All and all great guns for anyone who wants to shoot at a discount.