I've been fiending after one of these framesets for a few weeks now, and one appeared on craigslist for $290. It's black, has 400 or so miles on it, and has some etching in the top tube.

Is this a good price? Should I offer something?

It's an OK price to buy off of craigslist if you pay and pickup in person (so you can inspect). If you have to have it shipped, it's not enough of a discount off of brand new (about $400 -- see Froogle).