If you find a set of S13 coilovers for the front then you can always get some adjustable telescopic made for the rears. Somtimes you see coilovers going for cheep with a broken rear in the set.
http://www.silverstonetuning.com/pdf/KSX.pdf
And have a look at this thread for an idea of how much it would cost to get some springs wound up for you..
http://www.nissansilvia.co.uk/vbb/sh...rkshire+spring
Also don't forget that if you lower the Standard 12's they get a hideous amount of negative camber on the rear so you might want to look into slotting out your rear subframe...
http://www.club-s12.org/forums/index...20camber&st=20