My thoughts on surplus rifles:
- A "couple hundred bucks" and the ammo cost to feed it will mean a few hundred, or more, bucks spent. Feeding another "mouth" in the house will mean a continual/sustained additional cost.
- AR builds have become less affordable in recent years, but even still, $200-400 you'll spend on a Mosin and ammo to feed it would go a long ways (build your complete lower for that).
- You get what you pay for when you go looking for a wife in a house of ill-repute.
So my 100% no-spin advice would be to skip the surplus rifle and put the money to that AR-build.
If it's just a toy and you're looking to waste a lil money, then get the Mosin (because you'll be able to find ammo for it easier than the others) and knock yourself out. Tons of guys buy them (been through a few myself), tons of guys realize they wasted their money on them. It's kinda like buying a 1992 F-150 with 250k miles on it, just because you can get it for $500, you don't really end up getting much out of it before you realize it seemed better at the time than it really is.