DE's first pin, and one I still enjoy playing. Have a friend who picked his up fully working a few years back for $700, with only a few minor issues.
All comes down to cosmetics, and what they mean by "not working all the way" - get details on *what* is not working, verify the condition of the playfield, and especially the ramp - they are frequently broken, with no replacements readily available - be prepared to have to repair it yourself if you can't hunt down a good one.
If the game is booting and it's minor stuff (IE some lights not working, weak coils, etc.), and it's in good cosmetic condition, look at a similar price range. Start with less (IE $400 or $500 perhaps) and work your way up, depending upon condition. Post pic's and details on what's wrong with it, and you'll get a better estimate. Verify all the displays are working as well - at that age, it's not uncommon to have one or more that are outgassed/dead.