Follow Army GI's advice. It will be cheaper in the long run, and thats just in battery cost.
I've had red dots from across the price range, and none of the "cheap" ones has held up to moderate use. For what I spent trying out the lesser models, I could have bought another Aimpoint.
A real Aimpoint is a quality item. It wil take a beating and keep right on going. Their battery life is a non issue, with the shortest being about a year of 24/7 use, the newer ones are supposed to run up to around 9 years now. Even with the M2's, I dont even turn them off anymore.
“The enemy is anybody who's going to get you killed, no matter which side he is on.”
― Joseph Heller, Catch-22