I hate to advertise for ESPN, but a good way to get values of players is to look them up on the ESPN MLB homepage, click on players, enter the name, then fantasy, then click on all trades accepted.
Here is a link:
http://games.espn.go.com/cgi/flb/reques ... rIDTo=6420
1 for 1 trades in the last 15 days or so include: Bartolo Colon, Danys Baez, Kyle Lohse, Luis Matos, and Kelvim Escobar.
Frankly I think the starters in that list are too much to give up for him, but it gives you a good idea.