Car fan motors can produce up to 1hp, depending on the model. To put that into perspective, the popular Bosch 750W motors used to drive heavyweights are 1hp, and you wouldn't have much luck controlling one of them with a Sabretooth controller (or SyRen controller, the single channel equivalent).

I am assuming you need variable speed control? If not, then car fan motors can be operated by a relay or even a toggle switch moved by a servo (I believe this is the method used by Dragonstrike) and this control method wouldn't cost very much.
If you do need variable control, you'd be better off purchasing something like a Victor 883 or 885. They are more expensive but they would cope with a car fan motor (the 885 being capable of handling twice as much current as the 883)

http://www.robotmarketplace.com/products/IFI-V883.html
http://www.robotmarketplace.com/products/IFI-V885.html

Also, what Gary mentions about using some bolts to make a terminal block is a very effective way of distributing power throughout your robot and is one that I have used in all my robots since I learned about it. For a bit of visualisation:



The bolts at the top of the picture with all the wires and yellow connectors going to them are power distribution bolts (as I call them). Basically I take the negative battery connection and fit it to one bolt and fit the positive to the other. This way, my full power supply is available from these bolts. Anything that needs powered (drive ESCs, weapon ESC, LED etc) is simply bolted positive-to-positive, negative-to-negative to these bolts and then they get the power they need. The ones in the picture are maybe a little close together, a small length of metal falling across them could easily short the circuit. So maybe mount them a little further apart, wrap insulating tape round them when everything is wired up, and only use non-conducting materials as the mounting points for your bolts, not metal surfaces!