I've found that DDR2 memory is pretty much on a par with DDR now for cost. Seeing as that's where you're hitting your problem, why don't you sell the DDR to offset against the price of some DDR2.
I was even more optimistic - I was originally looking for a mobo to help me upgrade to DDR2 and PCI-e, but able to support my s478 Pent4 chip! Needless to say I was woken up with a few slaps round the face!