4.5 amps.... dude... thats some serious amperage. Thats more amps than what my 1000mh uses. No offense but are you sure you added that correctly? most pc fans are .3 amps max. how many are you running?
Couple of things you could do...
1 - get a power supply for a computer and plug the fan into that (as long as it had a dedicated line for computer fans)
2 - screw the pc fans and get a inline 500cfm fan from lowes (itll run you about 40 bucks) and its 120 volt. They also have a 250cfm fan for about 5 bucks less.
I personally do not understand the hipe with pc fans. I know a lot of people are using them... but seriously.. the dont put out that much cfm each and you need to dasiy chain a bunch of them together to actually get decent air flow. You could do the same from using that 1 inline fan I mentioned. Plus, pc fans will run you some money anyway. Why spend the money on a pc fan and inverter when you could purchase something that pushes a lot more air and doesnt need a inverter for just a little more?
Hope this helps.
Cheers