I've made several based off of a Tactical Machine jig (ar15) and Aim Small (ar10) using a harbor freight drill/mill and a bridgeport mill. With a mill you don't really need the jig, but it makes holding and drilling/reaming the trigger/hammer/selector holes almost idiot proof. You're not removing a lot of material although it will seem like it. If you can find the 80% lowers that have the rear take down lug pocket already machined you don't have to mill out the FCG pocket to meet up with it which will can you a little time. If I were looking to get a specific tooling for it I'd look at a used drill/mill or mini mill big enough to do it, but I'm biased towards machine tools. About the cheapest way into an ar15 lower is an Anderson lower. I've got several and they're ok.