Yep.

It gets expensive (materials and equipment).

What exactly do you want to cast? There are cheap ways to do simple things if you manage your expectations and are willing to repair/fix what you pull.

Just keep in mind, a good RTV silicone is about $125 a gallon, resin $90 and they have to be vacuumed for decent results. There's so much air incorporated when you mix, without vacuuming it out you'll always have bubbles and they usually end up in the worst spot. When I say vacuum, you need a true vacuum, 29 inches of mercury, not what a shop vac can pull off.

But if you just want to copy a box or something simple, you can get two part, hand mixable silicones that you stick together and jam on top, wait for cure then fill with resin. If you brush in a slush coat, then fill it up, you may get away without too many bubbles.

You can even get them at Michaels, but if you want the real stuff, google Smooth-On, they're the best in the world, I've been using their stuff for decades. Plus they're in Easton if that helps you. Go by their videos and tech support, not youTube if you want the right answers.