I was just thinking about this and remembered I did something similar with some house fans and TAPO last year, but it would cost around £40ish to get the controls set up if you don't already have some of the kit or similar gear.
What I did was have a couple of fans set to turn on when the temperature in one of the bedrooms hit X temp, then turn off when it dropped to X-1 for five minutes - the idea was to start getting some improved airflow to the room before it became uncomfortably hot but not rely on someone remembering to turn the fans on/off manually (and it let us use some very cheap and basic, but quiet fans).
Parts used were Tapo T315 themometer with display (already had as I was using some to monitor temperatures remotely) around £20-25 depending on deal, or a T310 which doesn't have the display and is about a fiver cheaper. The T315 has run for approaching 2 1/2 years on it's original batteries (bought june 2023 and is just starting to give a low battery warning)
A Tapo hub (although I think the Kasa ones also work with Tapo thermometers and plugs) H100 about £16 as the thermometers need it to link to the wifi (I already had one for some smart light switches and tapo buttons that we use for lamps).
A Tapo smart plug (packs of 4 are often around £25)
You can set the app up so that when the thermometer hits say 28c it will turn on the smart plug, then keep it turned on until a set period after the temperature drops, but you can set the "off temp" different to the "on", so by setting it to say: "On: 28c,
Off: 5 minutes at under 26c" you can stop the fans from spinning up for a minute then spinning down for a couple of minutes and repeatedly doing it.
There are probably cheaper ways to do it, but for a simple way that is largely fool proof* and allows you to hook up any fan just by changing what power supply you plug into the switch I don't think there is much that will be easier, and it's probably cheaper than buying mains fans with the function built in** as with this you could just get the cheapest quiet extractor fans and wire them up directly via a plug, or any standard computer fans and wire them to a mains adaptor connected to the smart switch.
I think you could also set the themometer to sound an alert/give you a notification on the app/phone if the temperature reaches a certain level, which could be useful as a warning that the cooling is not enough before the equipment has an issue.
*Do not plug the PC or other equipment into the smart plug...
**Extractor fans for example are very expensive once you go from a simple "over run timer" to say a humidistat, despite the difference being about 5 components on the control board, and the same board (sans extra parts) being used in the timer only versions.
