I can think of two nationally-significant archaeological sites in Central Europe - both were partially excavated about fifty years ago, to varying but fairly limited degrees, and then gently reburied, because there wasn't enough money to keep things going.

The site of one has a poorly-trafficked tourist centre today, the other is a clearing with nothing more than a tourist plaque. Both are likely candidates for previous capital cities, so they are obviously significant, but the money just isn't there to do anything about them. I seem to recall reading somewhere that over 90% of one of the sites remains unexcavated.

These are land sites, so relatively inexpensive compared to sea sites. If this is how willing we are to fund nationally-significant land digs, I imagine sea archaeology would be comparatively even more impossible to fund.