I've built I think 6 over the years. It's not too difficult, providing you buy decent parts and don't just buy the cheapest junk you can find. You pretty much do get what you pay for.
I'd strongly suggest buying a set of roll pin punches and a teflon receiver block to mount the lower into when you drive the pins into it. Saves a lot of scratches. I'd also suggest buying this book, one of the easiest to read and follow. Step by step instructions:
There are a few other tools you might want to buy, and if you only do the one build, you can sell the tools on this forum for about what you paid for them.
I would comment that you may not save any money building your own rifle, unless you get an exceptional deal on a barrel or complete upper, sorta like buying a car one piece at a time vs buying a car and driving it out. But you can put together exactly what you want in a rifle this way and that's worth something. Plus you will gain an understanding of how it all works together. Good luck.