I've had mixed luck with that auto 31 jewel Vostok movement - one still going strong (although it did have to be sent back to RU for attention), and another that completely gave up the ghost

Prior to certain geopolitical events they could be had for under three figures, which is a steal if you got a good one

The danger with the older ones is that the rubber seals might be toast - if it's an Amphibia this kind of defeats the object of a dive watch