Yeah then the 4 will work out for you.
i think you can get them as cheap as $5 each with shipping.
just need to get some old phone chargers with 3.5-9v outputs on them.
those fans should have the recommended DC needed. DO NOT EXCEED THIS #.
if it is 3.5v don't run anything over 3.5. You can cause a fire and blow the motor.
so be careful and make sure your wires are properly sealed and away from water.
especially if only using electrical tape....
Home Depot, Lowes, Walmart, and more carry this Heat Shrink Wire Wrap. you can use a blow dryer to seal up the individual wires and then both together.
They usually come in a few sizes so just make sure it will work out. and not just be a waste of money