Rebuilt boosters are running 450-500$ everywhere I've looked - if its even in stock. You'll probably have better luck buying parts to rebuild it yourself or send it in for rebuild. Meanwhile I've never seen those sold separate but rebuild kits replace the where items inside them.
I'm buying my parts from Rick Eskew at
http://www.remaninc.com/If I wanted it rebuilt I'd have sent it to "Booster Steve" at
http://boosterdeweyexchange.com/
