Not many sporty premium options in 18" under £100 I believe?
Blackcircles are doing a deal on Eagle F1 Supersports though bringing them to 112 or so each including delivery, so over budget but not too far out. That will be the next tyre on our BMW.
Supposedly immense dry weather performance while also being very good in the cold and damp unlike for example the Michelin Pilot Super Sports which is getting on a bit now anyway (great in the dry, bit sketchy when cold in damp/wet weather).
If you're not after a real performance tyre but something more allround maybe have a look at Falken FK510? Works really well on our Civic type S in 17". Comfortable with great dry and wet grip, just a bit on the soft side.