If you live in the US, the rapid tests are absurdly expensive--like sometimes $10 per test. Which also isn't great because rapid tests have a not-insignificant false negative rate, and, well, sometimes you just get a shitty test that straight up doesn't even work (i.e. the control line doesn't even show up).

I recently used this site in the UK to purchase some FlowFlex tests: https://www.visionpharmacy.com/products/flowflex-antigen-rapid-covid-test-1-test-kit

I believe there's a flat rate for worldwide shipping is £19.99, which is currently just under $26 USD. So larger purchases make more sense if you can swing it or split the cost of an order with someone else. So if you purchased like 50 tests, that would be like a little under $2.50 per test. Free shipping on orders over £50. I also used the discount code WELCOME10 to get an extra 10% off.

My recent order had an expiration date on the tests of October 2025, so, pretty good! But your mileage may vary.

As for why I suggest FlowFlex specifically, well, when the other two people in my household got COVID at the beginning of the year, on the very first day of both of them having symptoms, FlowFlex immediately showed a positive test for both of them. I'm pretty sure the quick detection was a big reason why I avoided getting infected myself (obviously the bigger reason was because of quarantining, but I digress).

My understanding is that FlowFlex is also one of the better rapid tests out there. An excerpt from their site:

The performance of the Flowflex COVID-19 Antigen Home Test was established in an all-comers clinical study conducted between March 2021 and May 2021 with 172 nasal swabs self-collected or pair-collected by another study participant from 108 individual symptomatic patients (within 7 days of onset) suspected of COVID-19 and 64 asymptomatic patients. All subjects were screened for the presence or absence of COVID-19 symptoms within two weeks of study enrollment. The Flowflex COVID-19 Antigen Home Test was compared to an FDA authorized molecular SARS-CoV-2 test. The Flowflex COVID-19 Antigen Home Test correctly identified 93% of positive specimens and 100% of negative specimens.

Obviously a few years old, so idk how well this holds up against the current dominant variants out there. I am unfortunately having trouble finding the original study, and I know anecdotes only count for so much, but yeah, these are the best rapid tests I've used so far.