Wellgo do some Magnesium body pedals that are very light for a flat pedal, cost £55, may be called the BAM96 or something similar, they're good! Or the Shimano DX is a very nice pedal.
Aah yes, if ever weights are needed I shall be there... Have you checked out Weight Weenies? probably not too many flat pedals on there, but an invaluable website none the less!