The Mobile SAM has been shown to be exceptionally powerful in small groups, being able to annihilate large groups of helis. While the cost could be increased, it seems like a few changes for now would be good and mitigate some of the OPness.
Changes:
-Replace quick-firing 2-burst and replace it with 1 shot per second.
-Reduce damage to 32. This will make it kill Apaches in 4 shots instead of 3.
-Reduce missile speed from 426 to 341. (This will also effectively reduce range limit from 12.5 cells to 10).