You'll likely get a bevy of solid,helpful responses shortly, but my advice is that you don't want to skimp too much with optics, especially the electronic/red-dot types. You don't necessarilly need to spend HUGE money, but you gotta get well past the tempting $99 range.
Rather than gettting something economical, that is likely also cheap and unreliable, you'd be better off getting proficient with your irons.
I'm more of an old-school KISS/iron sight guy myself,so I can't advise you on the best stuff around right now, but I'm sure some of the guys will weigh in with some specific recommendations.