Well, Sure Atlantic, the internet service provider on St Helena has possibly the worst website of any similar outfit I've seen. I can't find what they offer except "Bronze", "Silver", "Gold" and "Gold Plus" packages, ranging in price from £22 to £170 per month. What it doesn't say is how much data each package allows.
However, I do remember reading that the WHOLE island (4000 people) share only 20Mb/s satellite internet capacity, which sort of explains why they have to make it so expensive. In contrast, I'm sitting here in a smallish town in UK with 74Mb/s unlimited all to myself.
I believe they do offer unmetered data access during the night, but the speeds are all pretty miserable. Updating software for example must be a bit of a nightmare. Just a small update to iTunes, for example, downloads hundreds of megabytes. But don't get me onto the inefficiency of modern software writers - I come from an age where personal computers had kilobytes of storage and programmes of a similar size!