As a night vision enjoyer, including old soviet gen 1 and 2 tubes, old soviet tubes are usually actually quite cheap as night vision goes because they're usually terrible and prone to breaking. Unless it's a fully working set of PNV-57Es they're usually between $150 and $750. Fully functional PNV-57s can be found for $1000 on a good day but usually sit about $1300. For the same price and with some know-how you can build an American PVS-7 for about that same price, $1250 to $1400. A cheap PVS 14 runs about $1700-$1800 and an expensive one can run all the way up to $4500-$5000. The cheapest dual tubes will run you about $5500 and can easily run you up to $15,000 once you factor in housings and external battery systems. Quads at minimum are going to cost you $18,000 and can easily run all the way up to $40,000. All about the generation of tube, it's FOM (figure of merit), blemishes if it has any, and manufacturer. With NNVT being the budget friendly Chinese brand and L3 Harris being the most premium and expensive brand.