Well, I can't help if all you want to by is 1 pound of BP or one tin of caps, but...
www.Grafs.com, even with hazmat, the per pound price is cheaper than anyone sells it for. You have to buy 10 pounds though.
Walmart sells percussion caps around here, Remington #11's. Otherwise, I've ordered them from Cabelas at time when they have the " save $20 off an order of $150 or more" that covers the hazmat and you're set on caps for a long time!