I’d actually been looking at this sort of thing recently! Here’s a list of submarine tour links I had saved, though not all are deepsea. Note that I haven’t curated this at all, it’s just a bunch of links I have stored. I haven’t looked into most of these, though I did go on a shallow-water submarine in Cozumel. Think that went to about 100 feet? Really cool, but definitely not deepsea, it’s still proper reef. You do see a dropoff into the depths at the end of the tour, but you don’t go down.