This may not be the popular opinion with gear heads however If you don't put a heavy emphasis on aesthetics you can pick-up pretty much any large aperture red dot sight on the cheap (samples below). A larger aperture tends to improve your field of view which you may like at closer ranges. I've used these sorts of optics for the better part of 10 years with great success.
Companies tend to command a premium for sights that mimic premium brands like Aimpoint, EoTech, Trijicon, etc. If aesthetics matter to you, expect to pay anywhere from 50-100% more.
http://www.ncstar.com/product/produc...ies=Heads%20Up
http://www.ncstar.com/product/produc...s=Large%20Tube
Unless you're going with a 'real steel' firearm quality sight (multiple hundreds to thousands of dollars) they could all crack when taking a direct hit in CQB. You may want to also consider getting one of those plexiglass shields or kill-flash screens to protect the front facing lens if this is a concern for you.