"Lew" wrote

Are there any inexpensive sources for sodium metaborate?
-Lew

Tri Ess Sciences, Artcraft Chemicals, and Photographer's Formulary
are three sources of that inexpensive chemical.
Compounding it from borax and sodium hydroxide is less sure. Lye
has a great affinity for water vapor. Unless you've a lot of clogged
drains needing treatment, a large portion of it will likely turn
into a moisture laden block before it is ever used.
I've no use for lye in and of itself. Jorge has contended with the
moisture problem and may clue you in further. Dan