Unfortunately a quality clip on is very expensive currently, a collimated unit is around 12k and currently none have integrated LRF and are usable to magnification over 20x. Eotech and POT are the current top dogs but I think that will change soon with Nvisions new clip on.
I've played with the ones in the 5k range and they are junk IMO and are not user friendly at all. Resale is horrible as well.
Nvision is supposed to start shipping the one shown at SHOT this summer and that's exactly what i would be waiting for. It is fully collimated, integrated LRF, usable image up to 25x and American made, running off non proprietary batteries. 5yr warranty and supposed to be priced around 10k.