Is the backlight completely off or is it dim ??
there are a few possible problems with the backlight
1, the ccfl backlight failed - it would be easier to replace the whole lcd
2, the inverter died - replace the inverter (but sometimes a "new" (used) display assembly is cheaper
3, the inverter cable is scuffed - replace the inverter cable (search on ebay)
4, the inverter cable socket is loose - resolder it/find someone who can resolder it for you (in case you are not able to do that)
since the clamshells are sometimes pretty cheap to find on ebay - i would search there (got my blueberry clamshell for ~30$)