What's your usage case here? Portable recording, performance, being able to record a performance? Standalone use, or working in conjunction with another audio interface?
If all you need is the phantom power but have the other pieces already, you can get an
in-line phantom power supply (anywhere from $25 and up), though they do need need to be plugged in to a wall. But your mixer will likely be plugged in there too, so....
If you want *everything* powered off USB (mixer, mics, etc.) that might be a tougher climb, as the power you can draw off a USB port is limited.