I used to get my LSD's through engine importers. They would sell them for $200 or less, once got a tomei trax in pumpkin for $75, but the likelyhood of getting those deals is slim to none. The welded diff is for budget drifters, its not ideal for the street since the whole rear axel is locked and it makes low speed driving annoying. There is also the chance the diff could break the welds, this usually happens when drifting. I would look for a relatively cheap used clutch type perhaps on ebay or classifieds forums because when they come installed they make life a lot easier. Unless you or your bf plan on installing the lsd yourself.
Or you could just get a VLSD.
Here are a couple cheaper ones to get an idea...
http://cgi.ebay.com/ebaymotors...wItemh ... rs...wItem