Reddit reviews Pathfinder Society Field Guide (Pathfinder Campaign Setting)

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Pathfinder Campaign Setting: Pathfinder Society Field Guide. © 2011, Paizo Publishing, LLC. Authors: Erik Mona, Mark Moreland, Russ Taylor, and Larry Wilhelm.

Have you checked for alchemical items?

Fill the portable hole with water, use a Merfolk's Comb alchemical item: 750gp for a single use 8 hours of water breathing


The Pathfinder Society Field Guide has Air Crystals, which give off breathable air when chewed. 50gp for 1 minute of air. the comb is a better deal, as this gets costs 22k for 8 hours, if you buy 480 of them. Might be doable if you only need it short term.

The Advanced Race Guide has Elemental Breath, though it's only 1 minute per item, at 80gp per shot, that's 39k per 8 hours. This is definitely a more expensive item, and the other options are better.

EDIT: Actually, check this out.
https://www.d20pfsrd.com/magic/all-spells/f/full-pouch
You can duplicate these items, so if your DM allows the water breathing trick, you can get nearly infinite water Merfolk Combs for the price of 1.

EDIT 2: Ah, just saw that you want him to be crafting inside this hole, so filling it with water will not work.