If you like the milltek one, i think on a budget, you could find clearance stock prices for about £350-500, as they dont really sell them that cheap.
If you like the milltek, look at the systems on
www.cituning.com (i think its .com) they have them for something like £300 odd for the backbox and the center pipe, but milltek manifolds cost about £360 and they dont make them to 1 order - they only do them batch orders now unfortunetly!
Edit: also you may need to spend more money buying a decat pipe for it at another £70 + £14 carrage (dont know why they charge so much) it wont decat your car - but you will need it unless you can find a MK2 System of milltek.
Supersprint has a nice sound, unfortunetly its very common so if you want to go different - you have to go different by going more expensive, BTB are another good exhaust if you wanna have a different sound from every other saxo - and they sound the dogs balls.