e-bay
The "Duct Tape" batteries from China on e-bay are advertised as LiFePO4, but they are inevitably LiCO or LiMn if you are lucky. They are not as good at producing high current levels, but they cost half as much and they are better than SLAs.
Also, the motor output power will not exceed the input power no matter how high they are rated. The max input power is the pack voltage V times the max controller current A, and the max output power is V x A x E, where E is the efficiency.