First, check out FALFILES.com It is an invaluable source. Arizonaresponsesystems.com also has good info. I am on my second FAL build right now (a Belgian-made German G1 on a Brazilian Imbel reciever, confusing). My first build was on a DSArms reciever with pristine Steyr STG parts, the kits now are getting pricey as the supply of high quality drops. The G1 kit from Tapco is good dimensionally, but nearly 0% finish...Park job for 90 bucks. DSArms are probably the absolute best parts, but they charge you for it. My first build ended up around 1000 bucks, this second one is right up about 500. The Imbel is the way to go for a build. If you are going to buy a gun....ARS mentioned above sells great ones along with DSArms. Prepare for a wallet draining experience. Personally, I like building them. I have an intimate working knowledge of the gun and can fix most issues. The money I saved I put to mags and gizmos; new US furniture, scope mount, ammo..
For mags: tapco.com or interordnance.com good used mags for abour 4 bucks a pop...ahh the old days..
Good luck and in the end, you will enjoy the FAL experience. They are a hell of a weapon.