As Jay says, 500-600 is the starting point for a decent quality set with the adjustment you might need. There are cheaper ones around, but you get what you pay for.
Have you looked at the Suspension sticky thread at the top of the forum yet?
And have you searched or coilovers in this forum yet? There has been a lot of good advice and info posted in the past, including recommendations and
reviews
Spend some time searching for various phrases based around coilover, it's worth it