Im sure that you have all thought of this, but need to say it again no one makes a great living at UW Archaeology. Iv been doing work with the CT State Archaeologists and Historical Office for a number of years and have many friends at places from NOAA to Odyssey Marine Exploration (The dark side etc.) and have done Historical research and wreck consulting (paid and unpaid) for all of them.
Along the way I have found, or helped find, many wrecks of interest ranging from the Lightship LV-51 for the State of Connecticut and the Coast Guard Historian to the SS Republic for Odyssey lets just say the paid is much better then unpaid.
Think about how you will pay off any student loans and raise a family I just know of too many people with UW Arch degrees, never mind more standard Archaeology degrees, that cant make a living doing what they trained to do the number of full time and permanent jobs are very few, people who have them stay in them for decades, and the competition for those jobs is very fierce. Even Governmental jobs (Federal, State, and Local) can and will be cut as the budget managers decree.
I recommend that you get onto the Sub Arch web discussion list and read up on some of the job offers etc.
https://lists.asu.edu/cgi-bin/wa?A0=SUB-ARCH and here a a job site for UW Arch:
Underwater Archaeology and Maritime History jobs Pay attention to pay rates and employment periods. This list is also a great place to start making contacts in the field.
If you still want to go on, well have at it, it is a labor of love and we do need people who can do that.
I would add one last thing take some business management courses as this will give you something to fall back on. It will also help you in the career as sooner or latter it will not be diving, digging, and lab work it will turn into project management, audits, accounting, personnel, etc., and when you sit down with the people who control the money you need to know what they are talking about.
As for me, UW arch is an avocation, aerospace is my vocation and pays the bills.