Agreed H99 - you need a high capacity helicopter to make it viable and they are invariably expensive.
I flew back from there in 2020 in the Sloane 109 and it was already the most expensive commercial flight per mile in the UK, circa £250 for 28 miles. we went out by jet boat as the weather was poor, even in the middle of August.
If they can replace the Scillonian ferry with something faster and less puke-making, that would be the solution.
It's a shame because the 15 min transit in a helicopter is definitely the way to do it.