One simple and cheap way to grow worms and compost with them is a “sandpit” style worm farm. You just construct a structure that would be similar to a sandpit for children built on the ground. You simply need construct a sandpit, but don’t but sand in it, instead fill it with your compostable materials and then add the worms. As for building the sand pit, there are tons of different ways. Just search Google and you will find tons. Here is an example. Taking care of the worms is the same as in any other bin, like here.
If you live in a hot area be sure to build it where it will get some shade. Also be sure to keep it damp and fed well. A lip of some sort around the top will help keep worms from escaping. Be sure its deep enough to not freeze through during the winter. Check your frost depth and build accordingly.