Get a 4" vortex fan and a speed controler.In your small area that fan will be all you need.That fan has a 5 year warranty and there great.Quiet working and you wont have to worry about it not moveing the air.Those 12 voit DC fan dont have the static pressure the can fans do.The 6" vortex fan Has 449 cfm, .09 amps, 10 watts, 2600 rpm and dba 49.The static pressure is 0.84 in water.The fan pulls air 3'feet through the light {400w}through about 6' of duct through the fan and pushes out through 6" air conditioner flex duct about 47'feet to the outside vent.I dont have any heat problems with this fan.You can get a 4" vortex at PLANTLIGHTHYDROPONICS.COM for around $110.00 plus shipping.They are the cheapes on fans I know about.
Good luck with your project.