You want a spectra line rope - the big thick ropes suck because they bungiee back and forth. The Spectra is the really small (diameter) rope that costs about $90 itself. Also, get one with the nylon coating. Makes a world of diff when the rope is sliding through your hands.
If you're just begining, using the handle you already have is fine. It's not going to stretch much at all. And for just starting, money spent on other things (bindings/boards/etc/gas) is better spent than buying a handle. Once you advance and you feel that the handle is limiting you, then it's time to buy a handle. http://www.bulletskilines.com/
<- these guys carry the nylon coated spectra for like $59.. There site is down right now, hopefully it comes back up.