I guess I should have done my homework. I didn't think I could get a set of B&D dies for less than $90, but Grafs has them for $49.
Paco's website has an article, "Practical Wildcats", that describes taking a set of 357 Mag dies and converting them to B&D. He simply removed the temper from the dies, then reamed them with a .453 reamer ($5 at a local machine shop supply store), then polished the reamed sections. The only tricky part would be putting the correct angle on the front of the reamer to cut the B&D shoulder. Since used 357 dies are so cheap, I planned to do this myself using a drill press. I just can't figure out the best way to shape the reamer for the shoulder. If I could, I could still make the dies myself for around $20.