I've been sending 'em out for a few years now, but unfortunately am nearly out. You can buy them
Here for under $5 each. I'd recommend getting at least 3. That way you'll be sure to get a whole brick. They do crack occasionally when you're using them too. I don't really worry about that too much unless they don't hold together anymore. I've seen the miniforges wrapped in wire to hold them together, so others care about it even less than I do.