just put it on eBay and you know someone will buy it

A signed Derek Jeter bat is worth about $225 dollars (according to Tuff Stuff Collector Guide), so I'd say you could fetch about that (or more) for a signed jersey. Like anything though, you'd have to find the right buyer. Derek Jeter stuff seems to sell pretty good because 1.) he's a N.Y. Yankee and 2.) he's a sure bet HOF'r.