The prices on the link are not including VAT, so with the additional 20% your prices aren't far off, I would guess the stealers have put the prices up a bit as well.
Also bare in mind that if you just bond the skirts then you don't need the support strips.
The other alternative is R32 or ED30 skirts which are primered ready for paint but they will cost you in excess of £200 just for the skirts.
EDIT: You could try a Trade Parts Specialist as it may be a bit cheaper from them........