[Lou L]

Anyone know where there's a good sub manufacturer that could explore down to say 500'?

Whatever you do, don't get cheap with your purchase. A submarine is not something you pinch pennies on, especially not if you intend to take it down to 500'.

I'd stay away from nuclear-powered, as well. Too many maintenance costs.

[null and void]

One can pinch every penny and get a submarine that goes to down to 500’.

However, if one wants one that comes back up...