OK, who is going to ask Durex about the frequency response of their products?
If it doesn’t need to last very long (a month) or be exposed to high temperatures, a thin plastic bag from a shop may be a cheaper alternative to a condom. Unlike the alternative solution it has known durability: there is a lot of sources that discuss PLA degradation.
But I see a problem with all proposed solutions which are based on wrapping the mic in some kind of a bag-like thing: wind. If the cover is loose, the wind will make it produce sound. Putting it under tension would greatly reduce the effect, but would also cause distortion to the sound. You could put a muff on the whole device, but those can cost $10+ even if imported from China and I am guessing you are seeking a cheap solution.
Note: I am not stating that the idea others proposed is wrong. I’m just noticing a potential issue that has to be addressed.