Two weeks ago our local facebook page people were clamoring for rapids tests around New Years. They were hard to find. A pharmacy nearby had them, 2 in a package for $25. I picked up a package, should have bought two.
Last week, my son was calling around and there weren't any to be had in his area. I made one call and the pharmacy I called had a supply. $17.50 each. The following morning, in my son's area, the County was giving them out for free.
From the above, I gather that there is a supply of them, there just isn't an over-supply of them.
The demand also goes up and down. For example, a friend had a relatively large group of people at his house for New Year's Eve. He purchased a lot of tests, and each person was tested before being allowed to enter.