It doesn't cost a lot to get started. Especially is you're wanting to do blanks like you describe. I'd think you should be able to get started under $100. The biggest cost would be the mold. I'd suggest tube in molds from Fred Wissen (Ptownsubbie on this site). If you just bought 1, it wouldn't be to expensive. About $30 or so shipped.
His site:
PTownSubbie.com - Silicone Molds
Then there's the cost of the resin. I'd suggest getting Silmar 41 to start. You can get it from
US Composits, and it includes the activator. You can also get it from Places like Michael's or Hobby Lobby. But just make sure it's still in liquid form. Some people have bought resin that's already setup from a local craft store. That's the reason I suggest Us Composits. You'll get fresh resin.
There are some good casting articles in the forum library. I's suggest you spend some time reading there 1st, if you haven't already.
Have fun, and show us what you come up with. And if you decide not to do it yourself, there are lots of good casters around. I'm not very experience at tube on casting, but it isn't that hard. I'm sure if you ask, you'll get several offers.