Socket AM2/M2 boards will use DDR 2 DIMM sockets only, so you can say goodbye to DDR 1 memory. DDR2 sockets have been around for more than two years now, thanks mainly to Intel of course and their cost is already equal to DDR1 sockets. No change here.
THE AMD socket M2/AM2 based motherboards aren't likely to cost very much more than existing sockets. AMD advised its motherboard partners that the new motherboards will cost them only a little bit more. Socket vendors can make those sockets with small tooling changes to existing Socket 939 and should keep the cost to N almost equivalent level.