Primary Arms has a series of prism optics that are compact and seem to be pretty rugged. I have a 1x on a turkey gun that has seen quite a bit of use and abuse, and has held up great. They've got 3x and 5x options as well. They are not ACOG quality, but they are great options at less than half the price.
If you just want an enclosed optic vs open like a regular red dot, the Leupold CDS is a good little 1x scope for the money. I want an ACOG just because they are awesome but put the CDS on my AR because it seems pretty tough and it looks good, priced right and 1x is fine for my purposes.