Elicash: For a very average taxi, look at around $1000-$1200. Most, if not all playfields will be blown out in one way or another. You'll have sections that are protected by mylar, which will be a different color than the section not covered. Most likely there will be pop bumper wear. Also most cabs are a bit beat too. I see a lot with planking in the paint in the cabs, and sometimes planking in the playfields.
Take a look at the interconnect board too. Usually some sort of gi connector issue or hack. Easily fixable though. Make sure topper has light board and works.
There are a lot of taxis out there, so be patient if this isn't the one. It's a ridiculously great game. Just don't be afraid to pass on a beater.