I'm not too fond of the "sleeve" coilovers because of the fact that some of the perches are just made out of plastic. I think one of the most affordable coilovers out there are by Tokico. I've seen them as low as 799 for a full set and that has adjustable dampening.
Also, just like Accordcutie said, there are
groupbuys going on right now for the Tein SS and the new Basic coilover systems.
The difference between the SS and the Basic is that the SS has adjustable dampening while the Basic is just a height adjustable spring on a shock.