Are you talking about PCR tests, or antigen tests?
All I can tell you is that this week, my Aunt and I were both flying out of EWR. She needed a PCR test for the flight which was supposed to be Tuesday, and she started looking on Friday, but it was almost impossible to find anywhere with an appointment available before Thursday. And even those gave a very fuzzy 1-3 day estimate for results, which is quite unhelpful when you have to take the test within 72 hours of departure.
She spent an entire day trying to find somewhere which would take walk-ins, and eventually found a place through a fiend-of-a-friend-of-a-friend who could get her in, although she did have to push the flight back by a day.
From my perspective, this just seemed totally broken. I don't understand how there could not be a vendor, easily discoverable through Google which could deliver same-day or next-day results at whatever price the market would bear, even if it was $300 or $500 or whatever.
It felt like being in a developing country where things just can't be depended on to work properly.