Two 12v 30a relays from your friendly discount autoparts store, 20' of 12ga wire and some wire ends and you are done - less than $20.00. Cut the wires from the plugs on the bulbs and splice the 12ga to it or if you are really **** about your work like me take the bulb plug connectors out of the holder and solder the 12ga right to the brass connectors. Connect 12ga to R low beam wire stub at the R bulb, run the 12ga across the front of the rig, connect the L low beam wire stub to it and then a short run from there to the relay with a spade connector. Another spade on the other side of the contact points connection to battery. Connect the old power wire for the low beam to one of the coil contacts and ground the other coil connection. Upgrade the bulb ground wires to 12ga also. Do the same for high beam. Make the whole harness up and wrap it with electrical tape and it will be a professional looking job. I have done this on two rigs and it makes quite a difference.
To see how much you will gain put a volt meter probe in the bulb connector with the lights on and see what the voltage is, then take a jumper wire and go from battery to that connection and check the voltage.
Jim