You might search for other existing threads - boat taxes
have been pretty thoroughly thrashed out.
As long as you document the boat with the USCG and don't leave it in the states you should be able to avoid taxes, provided that the registration
address/your residency is not in one of those states that insists on picking the pockets of 'rich' yachties. It is easy enough to register it in Delaware - there are services that will set it up for you. There are other states that fit the bill as well. I am assuming that you are a US citizen; in that case it will likely be even more important to establish residency in a state without a state income
tax, or one that exempts its residents from income
tax if they don't actually live in the state (transients or foreign-domiciled).
It is also possible to buy a boat in a state with sales tax and not pay it, as long as the boat is out within the state's grace period and you are a non-resident. So I don't see that where you buy the boat is a big issue assuming the boat can be moved out quickly.
FWIW if you were an EU resident and the boat was VAT-paid then ownership
needs to be transfered inside the EU to preserve the VAT-paid status. Tax laws are pretty strange beasts...