Text from another forum I frequent-
If you shoot a musket in "577" and need a bullet mold for a very reasonable price, we're running a group buy at NOE for a 578 Hogdon Minie Ball mold. This is for a 4 cavity, yes 4 cavity. Thread is in the Active Group Buy section. You can choose your size based on what your musket likes, the group buy is for 575-582 diameters. Get in now for the discount. Finished price for a 4 cavity (you read that right) is about 133.
There is an active thread over on the NSSA forum-
http://www.n-ssa.net/vbforum/activity.php
The way to access this is to get on NOE's forum in the ACTIVE GROUP BUY section and enter "I'm in" with desired size in the RCBS Hogdon thread. I don't know of anybody making a 4 cavity mold for a 58 at this price with 3 interchangeable base plugs.