Later: Sorry - autopope points out that I misread this, duplexing is an optional and presumably pricy extra.
Meanwhile Morgans have two network colour lasers (not duplexing though) around £100-150, both look to be basic network or USB printers, 600x1200
Tally Genicon - £99.99 inc VAT -
Oki C3300n - £152.74 inc VAT - http://www.morgancomputers.co.uk/shop/detail.asp?ProductID=4281&CategoryID=99&SubCategoryID=199
Also a non-networking 2400x600 colour laser
Samsung CLP300N Colour Laser - £117.49 inc VAT - http://www.morgancomputers.co.uk/shop/detail.asp?ProductID=4279&CategoryID=99&SubCategoryID=199
Of course with all of these the problem is likely to be the cost of consumables over the long haul. But the idea that you can buy a colour laser for 20% of what I paid for my first 300 DPI mono laser is slightly mind-blowing...