Whilst some manufacturers are still predominantly making SDRAM, prices for DDRAM should be 50% more than SDRAM until the majority of RAM is DDR.
That's just my astute guess.
How do I work it out?- the price of things is so often what people can get for them. DDR is 2x the speed but for only 10%extra performance in a system. Those who charge more than a 50% premium will get undercut, and less than 50% will be silly because of the demand on >somewhat< limited production at the beginnning.
There will be a frenzy with the OEMs in two months' time!