The max depth for conventional scuba diving 130 feet - 40 meters - as dives to those depths can usually avoid complicated decompression procedures. This also covers the vast majority of underwater research deployments, and our work is focused there with our little falcon tube loggers. In keeping with the projects 'hardware store' ethos, household water filters offer a good solution for pressure testing DIY builds for deployment in that zone without blowing the budget:
https://thecavepearlproject.org/2023/05/24/a-diy-pressure-chamber-to-test-housings/