I think roller shutters may be substantially cheaper than blinds. The price of £2k I saw was for blinds. External blinds look a lot nicer than a security shutter. I have no idea why they are so expensive, though. I didn't spend a lot of time looking, so maybe they can be found cheaper.
Shutters rattle like buggery in high winds though.
There may be quieter ones, but no way would I countenance them for my gaff.

