You'll need to get either a set of springs and shocks, or a set of coilovers. Spring and shocks tend to be cheaper than coilovers, obviously depending on the brand you go for.
PhilJ on clubpolo sells cheap coilovers, and springs also i believe.
Also depending on the condition of your bump stops, it's worth replacing those while you have the suspension off, they're only a couple of pounds each.
Fitting is almost the most expensive bit unless you can do it yourself, or have a handy mate you can pay in beer