I am running an efan set-up on my truck. I am using 2 12" fans with a adjustible controller. It does help take load off the motor but I can't remember if it really helped mpg or not since I do drive it hard.
Cost can range a bit. If you go topend fans or junkard and if you go highend adjustible controller or basic adjustible.
I would suggest that you start looking online for fan options and see what numbers you come up with. You want max CFM with min amps at both startup and full power.
Past that it is an easy mod. Just make sure you have some SS washers on hand since you can't eliminate the mech fan pulley and you need to use the washers to take-up the thickness of the eliminated mech fan flange so you can re-install the nuts.