Is there a 5V version that can be powered by a USB?

Yes, there is a planned "mini version" that will be powered by 5V through a USB port. 

However, we are still evaluating how ready the consumer market will be able to accept a mini EzHotspot extender that will have a lower range coverage than the existing EZhotspot Extender. The universal rule is that electricity power = wireless transmission power. An incoming power of 5V/1A will never be able to match the performance produced by 12V/1.5A.

The EZhotspot Extender primary function is to repeat a weak wireless signal. If the supplied power is insufficient, the performance will drastically deteriorate.