A properly done SAS will cost that much and more! Simply selecting the proper spring rates & mounting points are challenge enough and if you make a mistake you're not returning those springs as new. I know someone who's got over 10k into his Sport's SAS !! Other's are in the 5-7k range (montero's, not sports). There are some who are in the 4k range but they're not happy w/ the results.

Of course I know if you're talking about going to a junk yard for parts and doing the sweat equity then it will be a lot less but then again properly done and inexpensively done aren't typically used in the same sentence.