Best cheap mixer

What would be the best mixer out there for under USD 300 preferably with usb.

Also, with a mixer, if I am using powered monitors, would I still need to run the guitar through a DI box before going into the mixer?

And the last question, which might be a fairly stupid one, if the guitar is going in the input of a DI box and then into a mixer, (a) do I just use output 1 of the DI box and then into one channel on the mixer or (b) do I use output 2 as well from the DI into a separate channel of the mixer or (c) do I use both outputs on the DI box and then into a split jack and then into one channel on the mixer? Never used a mixer before so I need to know how things are set up.