The cheap sensors are 2x closer at detecting change as they are at absolute temperature.
If your school has an Electronic Engineer department or a Physics department then check with them, they might know or cook up something you can use.
A pyrometer is based on rock that electrically polarizes when exposed to heat with the amount of polarization dependent on the temperature, sensitive enough to detect body heat. The expensive part is the electronics to read that as absolute temperature yet a PIR detector that uses the same principle gets around that expense by comparing output from 2 different pyrometers to look for difference. Suppose you had one looking in the hive and one outside, then if you have outside temperature known closely (1 expensive sensor) you can work with the comparative readings of many cheaper sensors inside versus the well known outside -- which would need calibration. You won't be able to use the PIR movement sensors as the two eyes on those are too close, but the principle may be something the physicists and EE's might get their own project out of.