You can make your own for well under $100, if you're so inclined. Check out the "Total Geekiness" thread if you haven't already. Lots of different options there.

Mine is two 12v, 20-w landscaping lights with a NiMH battery and smart charger. Total cost at just about $100 (if you don't count all my mistakes :-). Go with SLA (sealed lead acid) battery, and your cost will be significantly less, with a little more weight.