If you need to spin a fan, the most efficient way to do it is to have the engine run it. Using an electric fan is going to have loses in the alternator and the motor. So, an engine-driven fan will use less power than an electric.
, most of the time you don't need a fan! On my last truck ('98 F-150) I put in an electric fan and added an LED on the dash so I knew when it was running. It rarely turned on. As long as I was moving, enough air was forced through the radiator to keep things cool. The fan would only come on if going too slow on a really hot day or if completely stopped too long. So, an electric fan will use more power when it's running, but it won't be running very often. That is where you may gain a little.
Let's do some math!
I had a single, 16" fan on my old truck. It draws 11 A at 14 V, that would be 154 W or 0.21 HP. Hmmm, that's less than I thought it would be. An engine-driven fan uses not more more than zero when disengaged. No idea how much it uses when fully engaged.
As for the cost, the fan is now selling for $158. I think the controller was around $30. And then a few dollars more for a switch and LED (I like control!)