Yeah, if you want to stay on the cheap, check out Primary Arms. At least they are straight forward enough not to try to convince you that their stuff is as good as the real thing (although they do sell the real thing too). The knock offs that they sell are as good (if not better) than any other, but they stand behind their product and customer service is really good too.
Ultra Dot makes good products, but if I recall, their dot is on the big side and is more suited to action pistol shooting. You can get the Ultra Dot to the right height using either high or ultra high rings. The only other downside to the Ultra Dot is that it's not going to have that "tactical" look to the rig.
The bushnell is a bushnell. Some love 'em and some hate 'em.
Can't comment on the Fastfire, except to say that the combo with the Larue mount will run around $350, which kind of defeats the intention of staying on a budget. At that price, you could get a deal on a used M series Aimpoint.
I'd check out primary arms and get one of the Aimpoint knock offs if you are on a budget. If you are not on a budget, but are only considering those listed because you weren't aware of other options, I'd consider an Aimpoint M3, Aimpoint T1 or an ACOG TA44SG-10.