I've been looking to get a bit of aluminium sheet cut to size for a while and most places were offering pieces double the size i need for about £10 plus shipping, but if i wanted it cut to size (about half the size of the £10 sheet) the price suddenly went up to about £25 plus VAT plus shipping. More than double the money for half the metal just because they had to cut it!
Metals Direct UK on the other hand were very helpfull and offered me 4mm sheet cut to size for £10 including VAT and shipping, and even offered me 5mm or 6mm for the same price if they didn't have any 4mm in stock or if it might not be rigid enough.