Oh boy.
Everytime somebody asks what FAL to get, there's always a chorus of "build it yourself!"
Problem is, parts kits are drying up. And, say you can find a good condition STG kit. What if you don't want an STG rifle? What if you want a carbine, instead? Or a folder?
Maybe you have the gunsmithing experience to cut and re-thread a barrel, maybe not. (I don't.) Maybe you have the facilities to repark the thing, to make it look new, maybe not. Maybe you want a warranty with your rifle? You can, of course, send it off to many reputable smiths to have this work done for you, but that only adds on to the cost.
There's nothing wrong with a DSA rifle. They're the best FALs on the market, and their receivers are probably the best FAL receivers ever built. (Even the vaunted Belgian FN receivers were all cast after the 1970s. DSAs are forged.)
Yes, they're expensive. But price wise, they're in the same range as an AR-10 or a Springfield M1A, and people don't seem to be bemoaning the prices of THOSE.
Anyway, yes, you CAN build a FAL rifle. But unless you want a regular 21" STG type, you're going to have to get into some gunsmithing or order something else.
DSAs, as I said, are in my opinion the best. I've heard enough bad reports about Enterprise that I wouldn't buy from them, but you might have different luck. Weapons from Arizona Response Systems and Azex Arms have great reputations as well.
For a lower cost alternative, check out DSA's
STG-58A Austrian FALs. That's the type that mine is. They cost two to four hundred dollars less than a standard SA-58, if you don't mind the steel lower and a surplus (but excellent condition) barrel. They're available in standard, para, and fixed-stock carbine versions.
New DSA, or Imbel receiver-$400
Primo St G Parts parts kit-$400
Compliance Parts-$200
Assembly and park-$150 to $400
At a minimum, that's $1,150. I paid $950 even for my STG-58A, but that was back in 2001.