The SKS wasn't designed as a tack driver, it was a mass-produced infantry weapon designed to put lead downrange reliably. You're looking at 3-5 MOA on a good day, so I'd set a small budget and not expect much.

A 1-4x, 1-5x, 1-6x, or even a 1.5-6x would be fine, and I would put a cap of $100-150 or so.