Honestly more than $100 for more than one of these in good condition (but not yet restored) seems a bit steep... because odds are good you're going to spend some money fixing it up how you'd like it - so wouldn't you like to have more to spend?

I'd probably want to see it though before deciding.. maybe you can talk them down a bit on the price (pay close attention to the tires for example, if the sidewalls are obviously cracked and you know you'll need to replace them, that's something you can negotiate on.. tires will run you $20-60+ depending on what you choose).

You can also figure out how old it is by the serial number.. http://bruce.coppola.name/NishikiSerial.html On mine it wasn't on the bottom bracket though, it was stamped on the rear dropouts (there was a model number on one side, and the serial number on the other)... so be prepared to hunt if you don't find it right away.