If you're reasonably mechanically inclined, why not do it yourself? It's not really all that hard provided you have some screwdrivers, a socket wrench set, and a few hose clamps.
For me, I spent about $50 on a heavy-duty tranny cooler from Pep Boys and $3 for a brass barbed hose coupling. The tranny cooler I bought had the hose couplings and some extra hose already, and installation took about 3 hours. The items you'd have to remove is the protective cowl under the engine to gain acccess to the existing transmission cooler lines, and the radiator fan shroud to run the straps through the radiator fins to secure your transmission cooler.