Like anything sold online, prices vary...some dealers are "fishing", hoping you aren't going to spend the time to shop around- like you obviously did not.
$99 at Classic Arms:
Still $90 at AIM Surplus, but temp sold out, they'll have more...
And $100 at J&G:
Bud's has laminated stock ones- which bring a small premium- for $129 including shipping- so that's a pretty good deal; and I've gotten some really nice ones from them in the past.
If you have a C&R, there are even more wholesalers that you can buy from for under a hundred bucks.
There's still containers full of them on both sides of the Atlantic- there were over 18,000,000 of the 91/30's alone made. The hype about shortages and rising prices are just that- by people trying to create that impression to get more for their
Sure they might go up by ten or twenty bucks, big deal and what isn't these days...
The real issue may become if/when the cheap surplus begins to dry up. While I like the Mosin and have several (one of which has been modded to a long-range rifle), I don't think they've got too much further to go in terms of value as a shooting rifle when compared to modern production rifles- especially if the ammo becomes more expensive.
I don't shoot surplus- but a lot of guys do, and $.20/round for ammo makes for some cheap, high-power plinking. If the ammo dries up, the prices for the rifles will, as well.
When you can buy a more accurate, modern stick like the Ruger American for $300 that's a better shooting rifle that doesn't require a ton of mods to do it- the only attractive thing about the Mosin is the cheap ammo.