Coilovers are very expensive for the mk1-3 Polo's. Prices start at around £550 and the recommended Gaz or H&R ones are nearer £650 IIRC. Phil on here will be able to give you latest prices.
IMO coilovers on a road use only car are a waste of time. However, if you're actually gonna adjust them to suit different race circuits/motorsport venues they are ideal. At the end of the day, coilovers are just springs and dampers only made very expensive due to the fact of the integral hub/front strut design.
You can buy adjustable Koni dampers which are apparently superb along with a set of Eibach 40mm lowered springs give an excellent ride and handling compromise.
Your best bet is to PM Phil, he can sort you out with virtually anything suspension wise at very good prices.