Slacker, M1A's are fine rifles, but you're correct as to mag prices; surplus FAL metric mags are going for under 5 bucks all over the internet...
To me, to get an M1A that's the equivalent of an SA58 (or even DSA's STG-58), you'd be probably right around equivalent dollars. Current production springfields supposedly use very few, if any, surplus USGI parts; most have (again, supposedly) been replaced with molded metal parts. I'm betting an M1A with USGI (TRW) parts will be a price wash with the DSA guns, assuming you can find one.
I missed out on Steyer AUG's group buy of STG-58's due to a prior committment regarding last year's tax bill...once I unburied myself from that mess, I was able to get some bucks together for an STG-58. Dealer price, delivered, was $815 and my local kitchen-table ffl did the transfer for another 10 bucks. It's a BEAUTIFUL rifle and shoots just as well.
If you can find somebody local who'll do the transfer, I'd recommend it very highly. Somebody posted a couple months ago that if they'd had an FAL before their AR, they might not have bought the AR. I'm to the point of shopping FAL kits & putting a second and third one together. One will definitely have the Congo barrel. I'd say 'go for it'.
IM me if you have questions.
-hanko