Possibly a slightly rude question - I read about small islands in UK with declining population where government are trying to boost population, and it is more expensive to have people living there than mainland.
A big difference between the UK and the US is that in the UK council taxes are capped. There are bands, and the top band doesn't go above a certain rate.
In the US, there is no cap - you pay a percentage of the value of your house.
For example, in Portland ME the mill rate (the tax rate you pay per $1,000 value of your house) is $21.65. If your house is valued at $10 million, then your property tax is $216,500 per year.
Lots of millionaires want to have a big summer house on a Maine island, and they will pay $250,000+ a year property tax for the privilege.
No need for the government to subsidise the islands - the summer population is doing it for them.