I built mine about 10 years ago. Imbel lower, STG-58 upper with MINT bore, and a DSA receiver. I also bought a semi-only selector switch from DSA so you can't push the selector fully forward to the FA position (not that it matters but just for extra insurance). A complete spring overhaul kit was found at Falconarms.com. All the other tools and materials I needed I found from sellers on FALfiles.com. When I was done with the project I just sold the stuff I no longer needed on that same forum. The only thing I needed a gunsmith to do for me was pin and weld a muzzle brake on.
I don't recall how much total I have into it, but the parts kit was given to me by my father before he passed away. It was one of many, many machine gun parts kits he had. All of which I eventually sold off except this one FAL set that I wanted to build and shoot. Every time I bring it to the range I think of how much dad would have loved to see that I was able to make it an operable firearm again. He collected tons of stuff like that and loved to shoot, but never was mechanically inclined enough to tackle a project like that. I just wish I was able to finish it before he was stuck in the soldier's home for the rest of his days.