42DAY
Bit of a niche deal, but even at full price they have very good prices for desiccant and other shipment protection products, and sell to anyone with a credit/debit card or paypal in non-bulk quantities.
I bought some 500 g Esorb mineral dessicant a few months ago to keep in my 3d printing dry box.
Also worth checking out: 48mm tape dispenser and 2 rolls for $6.90 +del (after discounts).
The only criticism I have is that they seem to package their small orders of desiccant in ziploc bags, which are not quite airtight, so have a plan in place for where you're going to store your desiccant that you don't need right now. I used an old mylar filament bag.