Cheap way to on/off vents according to temp (to keep temperatures ideal)

So I'm using the fans on the A/C's that I was using this HOT ASS summer (90's on a lake in Ontario? WTF??). The temperature in the room needs to be kept down, but it's winter, so what is a cheap way to make sure the fan only goes on when the temperature hits my high point? I'm thinking like a thermometer-based version of a timer panel, ideally, but as long as it's cheap I'm willing to deal.

HI
I recommend going to any Canadian Tire the electrical section and buy their "Thermometer Controller" .around 20 to 25 bucks.It has a dual program meaning you can use it to turn your heat source(light)off when reaching to a certain degree or use it to turn the cooling fan on when temperature is higher than you programmed.It is the only cheap and very accurate control in the market.I use 2 of them to keep temp higher than 23 and lower than 29 .It has been working for 2 years with no problem . getting familiarize with it takes time but after you will be satisfied.
Just remember it takes a few minutes to operate and it is not instant response when you adjust it so be patient .

Would you be able to give me the brand name of controller that you use? And that is a beautiful dog in your avatar BTW. Thank you very much.

I tried to find the brand last night, there was none but dont worry.Canadian tire has just one temperature controller (i wrongly wrote thermometer controller the first time) .I appologize for that. you can find it just where they keep their "Digital Timers" in a panel in electric section normally beside the fluorescent tubes.it looks like a digital timer at first glance.
thanks for the avatar comment.He is 3 years old now and is a bless to my life.
let me know if this information did not work for you.