I purchased a Hannspree 1440 x 900 vga screen from Ebay for £24.00
confirmed it worked with external miniport to vga adapter in mirror mode.
I then removed the Mac LCD, disassembled the Hannspree, confirming that if one merely used the mac's ribbon cable it failed to boot. By extending the backlight cables, drilling the side rails to fit the screen and feeding the ribbon cable through the slot in the back I was able to internalise the Hannspree screen on the mac.(looks and works perfectly) The power supply and screen control buttons are taped to the rear of the Mac (A bit Frankenstein but who cares?) In all £28 rather than ridiculous price of a replacement screen. This has give the Imac a new lease of life.