Amazon have this Digimate 17″ TFT Monitor for £139.99 now. Add a keyboard and mouse for £9.99 and a basic Mac mini and you can have a flat-screen Mac for under £500.
(Though in fact I’d recommend adding a bit more RAM to the Mac, and going for the slightly more pricey Apple keyboard & mouse – total cost about £580 including VAT, or about £500 without)