Ovulation tests

What is the cheapest product/brand I can purchase to test ovulation? I’m using ovulation tracking as a birth control method (no opinions on that needed please). I’m aware this is a TTC group but figured ladies in this group would know best regarding this! I have seen tests in the stores but they seem to be sticks like pregnancy tests that are ~15 for just one test. I need to be able to take at least a few a month.