Hi,
the prices you quote for the UK are just outrageous. You might want to check a German site - they print decals at a pretty decent cost. Just a few examples:
http://www.druckeronkel.de/index.php?id=1015
They do print in white, metallics etc. Prices start from around € 11 for an A5-sheet (including p&h within Germany, probably a few € more for sending to the UK) for a print-out without white as a color (probably not metallics either), for € 15 (A5-sheet) white printing is included. He doesn't specifically mention metallics in his price list but you can assume that an A4-sheet includin