I voted "built own", but with an asterisk...
I don't have a FARS of any sort on my ISS. It's generally windy enough that we might need one only a week out of the year.
OTOH, a while back I built an experimental Davis based fan forced dry bulb/wet bulb psychrometer
. For that, I used a soil/leaf station, 2 temp probes and a Tee shirt hem for wicking, a 7714 radiation shield, and a 12v fan from a PC or something.
I needed more CFM from the fan to cool the wet bulb than a FARS would need. It seems like it could cost a lot less than the $135 that Davis wants for the DFARS kit to get a 12 volt "battery maintainer" panel (saw one on Northern Tool 1.8 watts for $15.00
) and buy or scrounge a 12 volt fan. Jameco has one 5.8 CFM for $4.95
, 1.1 watts.
NOTE: I pulled those items off the net as a sort of an engineering exercise. They may be too closely matched for the panel to drive the fan in anything but direct sunlight. But, you see how inexpensively it might be done.
Now, that electronic psychrometer project has been disassembled and repurposed to other things.