Here is the cheap optics I put on my AR15 (Barska ? ) I'm sure this is not the best but I am very very happy at the price. The veiw is very clear and the scope is made for an AR, seem more than OK in low light.
Most important it is cheap !
Here is a link
http://www.sportsmansguide.com/net/cb/cb.aspx?a=322930
If you want to see this scope perform watch my video and my AR15
http://www.youtube.com/watch?v=y-WYUzAIb-8