the currie motor is available for $65 at tncscooters. the controler is 20, the twist throttle is 8. the bracket is 15, and you could probably find some SLA batteries for 35 a piece.
Compared to buying the currie kit for 299, by the time you add it all together.....you'll have to ask yourself if its worth saving the extra money, and possibly getting yourself into a whole lot of technical dificulties.
My advice would be to buy the kit, then use tncscooters as a source of replacement parts.