The coil-overs that I want for the car are probably going to be in excess of £1000, so if I could find some used springs for the mean time that would be good. It's because I'm going to be putting on 18" rota grids, the standard wheels really let the S15 down I think, and I think it will look ridiculous at standard ride height.
Opinions?
The effort of fitting springs, and then going coilovers in the future you are better off keeping an eye out for a clean set of decent used coilys from Japan or someone in the UK.
I have used Nengun's used parts/yahoo auctions before. They are very good and will test the suspension for serviceability for you before sending it on if you buy used parts from Nengun direct (not necessarily yahoo auction parts though.) You can probably get some used HKS ones for 600-700 landed with some peace of mind. The lack of salt in Japan probably means they will be better than UK used.
Either that or if money is tight have a search about for used S15 factory option S-tune suspension. Go for the silver and red ones, not blue and yellow, they are older.