Whilst Killik offered an investment scheme, may offer private cask ownership.
The true unicorns of this world have been casks from Springbank and Bruichladdich.
In 1998 you could buy a barrel of Springbank for the following prices:
Refill sherry hogshead: £1,150
Fresh sherry hogshead: £1,250
Fresh port hogshead: £1,300
Refill sherry butt: £2,300
Fresh sherry butt: £2,500
Fresh rum barrel: £900
Considering a 1998 vintage 26yo Springbank sells for £1000 a bottle today, that's a tidy return!