The extended storage of the fancy stuff involves it being aged in the barrels, undisturbed and left mellow. Even for something like an 8 year old Scotch compared to a 12 quid bottle of Lidl/Aldi own brand - the costs of storing the stuff for years, sometimes decades, is going to be a large part of it. The ageing/mellowing has to be done in the barrels - it can't be bottled and left to age as that doesn't work. If anything the 8, 10, 15, 20 year old stuff has to be distilled to a higher alcoholic volume as a during the lengthy maturation/mellowing process some of the alcohol will evaporate - ageing is to improve and mellow the flavour, it does nothing to increase the alcoholic volume.
In addition to the obligatory fancy bottle, labels and also be the 'small batch' costs to consider - there's little point in making large batches if not many people can afford to buy it.
Obviously if something is 'fashionable' for whatever reason sellers will take advantage and inflate the price but that applies to everything.
I'm lucky as I'm a chav who dumps loads of mixers in everything so I stick with the supermarket bottom shelf.