Warfarin needs blood tests at least every 2 or 3 weeks. I bet those tests are not cheap in the USA. Furthermore you can't have any food with significant amounts of vitamine K or its precursors. There are pills that cost more but don't require any of that. And actually they cost very little or zero, at least in my European country. Prescription only, of course.

>I bet those tests are not cheap in the USA.

Within 5 minutes of searching I found a PT time with INR test for $24 [0]. Add in the testing fee and it's probably around $30.

[0] https://www.ultalabtests.com/test/prothrombin-time-with-inr-...