Is rug hooking difficult... or expensive?
Learning to hook rugs is one of the easiest things that you'll ever learn to do. There is really only one stitch to learn and if you make a mistake, you simply take the stitch out and re-do it.
I wouldn't advise starting out hooking a detailed rug with a lot of shading, etc. or you might get discouraged. Start with a simple pattern and work your way up. After all, when you learned to drive a car, you didn't start with a new Mercedes (I hope)!
As far as expense goes... it's the same as anything else you learn to do. You can spend as little or as much as you want. There's different prices and qualities for any and all of the things you need to hook a rug.
You can use "re-cycled" wool, gathered from friends, thrift stores and garage sales or you can buy new wool which is, obviously, more expensive.
The same thing goes with your hooking frame and the way you cut your wool... you can spend a great deal or start out cheaply and work your way up.