Late 70s, early 80s SS pins are my speciality! Yes, SS is the right term for this era of "Solid State" machines. After Electro-Mechanicals (EM) at around the mid-70s but before the DMD (Dot Matrix Display) games starting in the early 90s.
I've got 3 SS games, all Bally: PARAGON '79, VECTOR '82 and GOLD BALL '83. Both PARAGON and VECTOR were bought as non-working projects from members of this forum for £150 and £125 respectively. Neither worked at all when first powered-up except a few static lights, but it took just a couple of weeks doing a few hours an evening to get both working again. PARAGON is now the subject of a total strip-down restoration and GOLD BALL is having a "flash makeover" to get it into fully playable condition. VECTOR is the only pin I've bought in working condition and I still think it was an absolute bargain for £350 (not sure the seller is a member on here but he's friends with people here and is on the Yahoo ukpinball group). I've fiddled and tweaked a few things on VECTOR (all pins require TLC, even brand new ones) such as flippers, tightening loose screws and nuts, broken wires, lamps, rubbers, bit of polish, etc.
(If you want to see the sort of effort involved have a read through of my Shop Logs linked in my signature below)
Basically, I'd pay around £100-150 for non-worker but where I could see things can be fixed. Ideally a working SS that needs some extra TLC around £200-400, and a good worker around £300-500. But it also depends on the game. VECTOR and GOLD BALL are not classic titles; no one is going to shell out for either of those no matter how good the condition. PARAGON is considered a classic (it narrowly missed be Pinball Arcade's next table) so a good one could be £1,000. Expect to pay silly money for some of the classics though. I've seen a totally trashed project CENTAUR fetch £600!
But one thing I've learnt since getting into pinball less than two years ago is that games are full of surprises. Lesser known titles are still a whole lot of fun to play. And you can use any machine to learn your flipper and nudging skills.