paid up members get about 25% off tyres at Camskill.com who are generally cheapest anyway. Can definately recommend them, been using them for years.
Wish I'd known that, I've bought 3 for my ZS from them recently, highly recomended.
I then used blackcircles website to locate a local fitting centre to put them on.
From what I remember the Yokohama S Drives were specifically designed for the MX5. I don't know if that makes them good though.