affordable calibration microphone

Hi everyone!
I am an audio enthusiast, and this last year I have been getting more and more into this world, specifically in box design. I don't have many tools to measure different things, such as the Thiele-Small parameters, which I was able to measure on my own with a circuit I made. But over time, I have realized that I need more tools to be able to reach the objectives I want, such as a calibration microphone. The problem is that I do not dedicate myself to this, nor do I plan to do so, at least not for the next few years, so I am not going to buy tools as expensive as a UMIK-1 or UMIK-2, or the Dayton Audio DATS V3 , since I don't have the ability to buy things at that price either.

My question is if there are cheaper options, specifically for the calibration microphone, I would like to have one. And if someone recommends other tools that could be useful to me, and that are not very expensive, I would appreciate it.