I would wait. I doubt it will sell at that price. Maybe offer him 250 and to let you know when he is serious about selling it. Depending on the number of speeds, there are a few people out there (you can find them on ebay) that will overhaul old STI shifters for like $40. But usually in the old ones it was just a lot of gunk. Please use something like GT85 and NOT WD40. WD40 is sticky and isn't so much a penetrator as rust preventer.
I have a number of older shifters I have had to spray out with GT85 and then they start working like new, so I wouldn't say no just based on that, especially i he says he freed it up.