Let's take these one by one:
'will probably go up 10 fold'
Even if it does, which I doubt, then each will cost $800,000. Put 10 onboard and you have $8,000,000.
'having to be made of metals that don't corrode as quickly in the salt water.'
The U.S. navy has battleships that have been in this 'corrosive' salt water you speak of for 60 years. They're ok so far. FYI, keep a little known item called paint on the metal and you're good to go.
'The maintenance on the machine will sky rocket due to exposure to salt water'
How do you know it will be exposed to salt water? I highly doubt the machine will be just sitting on deck.
'The life expectancy of the machine will dramtically decrease due to salt water corrosion.'
Again, see the 2 points above.
'Will an investor make a decent return on his money investing the billions it will take to do it'
Again, it will not take 'billions' to do it. A whole lot closer to $10,000,000 to retrofit as opposed to your 'billions'.
I predict future happiness for Americans if they can prevent the government from wasting the labors of the people under the pretense of taking care of them.
-- Thomas Jefferson