Yes, I built an STG58 kit on an Imbel receiver. It's not as easy as an AR, but it can be done as an at home project. Whether you save any money.....I have no idea. I bought the parts kit and receiver sometime in 1996 or 97 - no idea what they go for now. There are FAL specific tools for assembling the receiver and barrel that you will either need to build yourself or buy. You also have to worry about the MA assault weapons ban, and 922r imported parts compliance. You will need headspace gauges, too.
This was the project that kept getting back-burnered for years. I finished it (well, functional finished, I haven't made up my mind about refinishing yet) last month. It's a fun rifle, now that every piece of the gas system has been replaced. I'm not sure I'd do it again - I don't like it as much as a 308 AR. Glad I did build one, though.