For a budget RDS, the PA MD-ADS is the one to look at. 50k hr battery life, it's been tested quite a bit on the ARF, M4, etc... forums and it seems to be pretty robust.
It's basically a Holosun with the old quirks worked out.
I keep hearing it's not as dependable as an Aimpoint, and I'm not arguing that it is.....but I haven't seen why it is not. There don't seem to be any complaints regarding reliability that I can find, and normally, if something is failing, you hear about it on the forums. Everyone that has one seems to be pretty happy with it.
I had one that I had to send back. After a few weeks of leaving it on, it lost about half of the brightness settings. The dot was still there and it was still holding zero. PA took care of it, and the replacement has been working like a champ. That is what makes me leary of saying it's on par with Aimpoint. The Aimpoint PRO and H-1 I have bought haven't had any trouble, though no company is flawless.