I'm in the process of building a 1911 in 38 Super from scratch. I too wanted to approach it as a learning experience. I bought a Caspian Frame and Slide at Camp Perry last year. They were seconds, and only cost me $225 for the combo. Even so, I will have pretty close to $1000 into it before I send it off for blueing. Add to that $1000 worth of tools and jigs from Brownells, and another $300 for tools and jigs I already had. I have learned a lot in the process, but there is nothing about this that was a cost savings.
If you buy a matched frame and slide that have already been fitted, you can cut back on some of the tools required, and you can buy drop in barrels and bushings, but you won't end up with the same gun.