Your voltage and current (therefore, power) requirements dictate the transform's power rating, i.e., 480 watts. There's no magic bullet to get around needing a transformer with that output capacity.
As an alternative, I might suggest getting two cheap or used 12VDC automotive battery chargers with at least 10 amps output capacity per charger (even higher output current capacity would be better), connect their outputs in series and use that for your power supply. These units are not all that well regulated, but given that you are driving a motor, regulation ought not be a major concern.