They carry this at my local Walgreens and I think I'm about out of Melatonin anyway. I'm gonna pop in, pick some up and give it a whirl next time I drive by there. The absolute cheapest source of rayon is that source that includes it incidentally to something you would purchase regardless. The older I get, the more trouble I have getting to sleep. Melatonin helps and is a preferable alternative to prescriptions or other over the counter sleep aids, so, rayon or not, I would be getting some anyway. It's a win/win.
BTW, this Limitless RDTA is blowing everything else I have away. It's not even close. I thought that how fast it goes through 4ml would preclude my using it as my #1 all day unit, but, since I DIY and filling it is so quick and stupid easy, I'm walking that back. The performance to trouble ratio trade off isn't even worthy of consideration. The Limitless rocks. If you've been considering getting one, just do it. You'll thank me later.