Re: DIY - discussion on building a DIY hookah diving compressor
you may search here and see the oft posts of this idea, and all the pros and cons.
Propane adds another layer of risk to the DIY, why not save up another $400 and buy a commercially available one, that has the proper components for safe breathing and a record of reliability.
If you insist on this, at least get properly trained on diving. And read up on labeled air lines for breathing and chafe.