Supply & Demand
Ever been to Simpson Ltd's store in Illinois? I could spend hours in there.
I think there is a difference between bulk surplus and surplus. Nagants, SKS's, & Mausers, & Enfields were cheap back in the day because they were available in bulk. Bulk surplus is bought cheap and sold cheap on that 1st go about in the market.
Now that all those guns are in private hands (no more bulk surplus) the price increases, doubles, triples, etc. They are now into a 2nd market where there is no more piles of rifles readily available.
I do note that 03 C&R guns always seem to sell for more $ than guns sold through 01 dealers. The idea that you can have a C&R handgun shipped directly to your door somehow means to sellers that it should be priced higher than the rest of the market.
With antique guns (no FFL required) that is even more the case.
Note I don't have an 03 license and except for that one visit to Simpsons Ltd - don't think I need one.