https://www.homebrewtalk.com/threads/diy-fermentation-chamber.679010/
https://aussiehomebrewer.com/threads/foam-fermentation-chamber.89513/
https://www.thehomebrewforum.co.uk/threads/diy-temperature-controlled-fermenting-unit.63088/
theres litereally hundreds of threads on this exact topic on multiple homebrewforums. people are very creative diyers and frugal and just about every kind of ferm temp controller has been thought of and built already.
have you ever thought of going chamberless
two low cost options are:
ball and keg :
and what i do :
View attachment 835849
View attachment 835850
i pieced this together from morebeer
i can get this thing down to 20 -25 degrees below ambient temps by changing out frozen 1 gallon water jugs once per day. it can cool about 1 degree every 4-5 mins when the pump goes on. changing the frozen jugs once a day are a pita. but it beats needing a dedicated ferm fridge. my basement right now is only about 64 degrees and i find that the pump rarely cycles. only late at night after the jug has melted do i find it going more than a few minutes and then i change the jug anyway . and if you got the funds you can always attach a glycol chiller to it for an upgrade. or if your are handy you can convert an old ac unit into glycol chiller. and totally diy it.
i can even cold crash with this to about 40 degrees by just putting ten pounds of ice in the cooler when i need to prior to packaging.
theres many options for temp control other than ferm chamber builds. i felt this was easier way for me and im not handy enough to build the foam thing. i put my temp controlled fermentor together for less than 100$ including the FV.
cheers