If you have a very large res to get it even cooler you just add frozen 5 gal or what ever that would fit your mini frig and your coil around it . the cost is only the mini frig running is very little. and you can use it for more that 1 purpose
just add a small water res that fit inside the frig at lest 5 gal add a small fish pump run a recir line from small res to a hot box or a car heater core put it next to the intake on your hood light
so now as your fan pulls the air through the hood light it goes the the hot box or car heater core its cheaper that a hot box
cool your temp way down
and if you want even colder just add another heater core with a fan with a temp controller have it run the fan as a air conditioner