I own a couple of Garands, a DSA SA58 and a PTR-91. They're all fine rifles. Based on your statements above, I would strongly encourage you to get the PTR-91. They are exceedingly reliable and accurate rifles and are great values at a street price of around $700. In addition, as others have pointed out, the mags are "disposable cheap." You can buy mags for as little as a buck each. As a result, I have far more mags for my PTR-91 than I have for any of my other rifles.
Just to be balanced, though, here are the disadvantages of the PTR-91 (and any G3 clone):
1. no last-shot bolt hold open
2. some find the ergonomics to be awkward (safety position/reach, charging handle location, etc.). The mag release is really awful. The G3 had an AK-style "paddle" mag release that worked well, but part of the ATF-mandated changes in the semi-auto variants like the HK 91 and PTR-91 was elimination of the paddle mag release and replacement with a push button on the right side of the receiver. As a result, changing mags is a two handed operation unless you replace the stock release (see below)
3. typically VERY BAD triggers out of the box -- very gritty and heavy
4. chew up brass real bad thanks to the fluted chamber and, ahem, "assertive" ejection (so forget reloading it)
5. accessories are a little harder to find and more expensive than those for the FAL types rifles (and way more expensive than AR or AK accessories)
Some of those "faults" are correctable. Bill Springfield will do a great trigger job on your PTR-91 for $35, and all you need to send him is the trigger pack (which you can remove in about 10 seconds by field stripping the rifle). There are a number of places that will install G3-type paddle mag releases, but they're expensive. Alternatively, you can install a Tac-Latch, which is almost identical to the original G3 paddle mag release except it moves sideways (instead of fore-and-aft) and you can install it yourself for about $35. Also, accessories for the PTR-91 are becoming more common and more available every day thanks to the incredible popularity of the rifle.