Variable speed fan controller (electrical gurus help me)

What I wanna do is build a variable speed electric fan controller for my main (electric conversion) fan. Instead of just kickin on full speed or being off completely I want somethin with more control over my temp. Flex-a-lite makes one and it's 95 bucks... which is a complete rip off for what it is. I mean, the main components are a temp probe and a variable speed controller. However, the stuff between the two is where I wouldn't know where to start. It would somehow have to be programmed. Somehow I find it unlikely that this would be really hard or expensive to build. So how would I do this?

Here's flex-a-lite's overpriced junk.

I'd look at the speed controllers for electric scooters, you can find them on ebay. I think they use a pot for the throttle input. How does a temp sensor work? If it's variable resistance and it moves in the right direction you may be able to use it for the throttle control along with a resistor to set where it turns on. But it probably woun't ramp up quickly enough, so you'd be stuck modifying the signal anyways. And I don't know much about that.

That makes complete since, I just need to know how to build it lol :confused1. So I'd want the fan to kick on at 160 (my operating temperature) and then be directly correlated to the temp probe past 160 and be at 100% at say... 180? So how would I program that? I'd need a speed controller with the same bandwidth (or whatever you'd call it) as the temp probe so that it would only take twenty degrees to send the fan all the way to 100% speed. Plus the resistor or whatever I need to set the initial start temp (160) and I'm good to go besides knowin how to wire everything up right?

It's over my head. I'd be inclined to go w/ a 2 speed unit. No real need for infinite variations. And I'd probably set low at 10* above the thermostat opening and high at 10* or 20* above that, so something like 200* and 220*.

Right now I'm running just the stock electric fan, no mechanical. I plan to add another electric fan, but it hasn't gotten hot enough yet to require it. The single electric almost never comes on as it is.