hi viklash.... heres my ten bobs worth.... i built somthing similar to carry an SLR but it was for a stop motion animation i was doing so it was hand cranked.... i used a builders level for the rail, cut a toothed printer belt and pinned it to one of the sufaces of the level, used one of the printer pullies as a drive and four small bearings ran on the inside of the builders level... super light weight

if you want it driven.... id use an RC servo with a servo tester with battery pack... dial in the speed and a away you go... your audio will be goosed by the servo but im guessing you allredy knew this

it shouldnt cost you much more than £50 in parts excluding the printer belt and pully.... if your interested in this low tec version let me know and ill try to get some pictures to show you what i mean (its stripped now but i still have most of the parts)