They are fairly easy to make, once you have a wood lathe and some skills working with wood. The exotic woods are very cool, but some are a pain to work with. The "voices" for the calls are available online, but they all need tweaking to get the right sound; so this takes practice and a good ear.
Like most things these days, there are some good online tutorials out there, and a few books to get into the intricies of shape and sound.
I find it a lot of fun and extremely rewarding when you call in a coyote with a call you made yourself.