Best to go to the Dahon site and look up their "Sport" bikes. The Speed Pro weighs about the same as the Rocket and has 21 gears (SRAM Dual Drive) but not drop handle bars. The Helios SL weighs about 4-6 lbs less than the rocket, but has 8 gears and again not drop handle bars.
I have the Speed 8. It is a great bike for what I do. I am not sure that I would consider it the equivalent to the Pocket Rocket as it is not custom made for my size and is heavier than the PR. Of course, it also costs less than half.
You might also check the Dahon Msg Board on their site under "Community" and see what modifications some Dahon owners have made to their bikes.
Regards,
Gary