Titanium is nominally about $40 / lb to make from ore, so the cost won't be too inexpensive if you just made a dinghy
Titanium is not hard to drill or work
at all and does not require a diamond drill bit. It's tensile strength is as strong as low alloy steel
but 40% of the weight yet twice as strong as the better grades of aluminum
yet 60% heavier. It really fits between steel
in terms of structural properties. It is not stronger than steel just lighter. It's primary use is in white paint
pigment not as a pure metal.
Chain plates and other critical pieces of the boat hardware
would be nice in titanium. If constructed much like an aircraft hull it might prove to be a good hull material but with a hideous price
tag. It's great stuff in sea water
but it's not magical. It is a strange metal in that it will burn at 610 degrees C. When used as a metal in structural applications is is alloyed quite a bit. Another neat property is that is colors easily.
It would not be any more immune to sea growth than anything else. It just would not require a barrier coating except to help bond the bottom paint