The easy way is to punch them into Gun Broker and see where auctions on those items are running.
The only one I can speak to directly is the Yugo SKS... with the grenade launcher, it's a 59/66, and if in great condition it can probably bring no less than $350... right now, maybe closer to $400.
The Chinese one will likely go for about the same price. While Chinese ones tend to be priced a bit higher than Yugos (they were a bit nicer), the wear likely knocks it back a bit.
The Taurus sounds like a model 85, but I'm not sure where a used one would price at... a new one would go for somewhere in the $400 range, so maybe lop a third off of that or so.