Lurecraft.com has a
huge selection of the cheaper silicone molds as well as finer detail aluminum molds that are more expensive. (Stay away from their plastisol).
luremaking.com has fine quality molds.
There are some good deals on EBAY - many from overseas and free s/h.
Baitmold.com is one of the companies that supply molds on EBAY.
Do-it molds have quality molds.
I started out making my own molds using plaster, but only one side open pour. After a while I figured why not make two-part molds with full round cavities. Plaster of Paris did the job. Recently I found a plaster used for artwork that produces super detailed copies. Both materials will copy what you want at the lowest price. Silicone is more expensive and a bit harder to work with but produces good copies.
Just be careful who you buy plastisol from. I get consistent quality from
M-F plastics. Just know what plastic
firmness you want : soft, medium or firm. Most companies sell at least three grades. Then you'll need different dye colors and flakes. Clear lures catch fish, but get a bit
boring to use after a dozen fish.
Getting started is never cheap nor economical unless the lures from those molds are the only ones you'll consistently use and make to your own specifications. Of the 40 molds I own, I use maybe six/ year and only as a supply of parts for different lure types. But then again, most hobby craft is that way - just another expensive way to collect
dust collectors.
