prices can range from anything from £600-2k for a S13, 1k-5k for a S14 and S15's are silly money. i bought my S14 Import for £2300, 60k on the clock, 20bhp more on uk s14's, only down side its a auto, but i picked up a full manual conversion kits, including pedals, box, clutch, fly wheel, etc etc for cheapness of £180. fuel is really bad on short journeys, but i only use the car on my days off work.
unsure if you know, the imports came in classes such as Q's and K's. K's where the top level of spec. Q's = Queen K's = King.
they are very easy cars to get alot of power out of with a small amount of money being spent on them.
enjoy!