AR's are fun to build and shoot. If you build it yourself, you could do it for relatively cheap, but the range snobs will slaughter you if they find out that it is a "frankenAR". The platform is very versatile, because of it's modular design. Get a .22LR conversion kit for the AR and you can shoot it for cheap all day long. Like a big bore? Get a beowulf or 458SOCOM upper. Like a long range rifle? Get a 6.5Grendel upper.
FAL's are great battle rifles (probably the LAST great battle rifle). As mentioned, DSA makes a GREAT FAL - I like the PARA versions a whole lot - at least the ones' I've handled and shot. My favorite FAL is still the South African R1 - can't beat them for accuracy.
M1A's are fine rifles. VEry accurate and easy to shoot. I really like them, but I'd have to say, go with the walnut stock - the SOCOM version is a great "tacticool" rifle - it is still accurate, but it just does not look right.
All 3 are great choices, but you'll end up shooting the AR more.
