It's just ridiculous isn't it really? I can't count the number of times someone has recounted to me a tale of being horrifically overcharged for a product that is distinctly lack lustre, simply because they were choosing to forego alcohol.
It's common knowledge within the industry that the mark up on soft drinks is often used to make up for the keen pricing of the start products which venue owners assume help decide whether or not someone goes to their bar. A glass of post mix costs approximately 4p in ingredients. Now it's vital to bear in mind that the costs to the bar own don't end there. They must heat and light the space, provide a chair to sit on and a friendly ear to pour your drink and hear your woes. Nevertheless it seems supremely inject that these gains in mark up are used to make up for charging a lower price to those who are drinking. This will surely change under the weight of demand.
What interests me though is quite what an alcohol free drinker is looking to pay. The KAM and Lucky Saint research suggests that quite a number of people choose not to drink alcohol in order to save money but this may not prove significant. It is true that alcohol free drinks don't pay duty so they should be slightly cheaper. Conversely, many alcohol free drinks can be labour intensive to produce as the alcohol has to be removed. This of course makes the product more expensive.
I suppose it remains to be seen where people sit on price elasticity but I think the most valuable take away from these stories do not relate just to price but to perception of value. That includes the product being post mix but also the glassware used and the range that's available. If you think about it, if you're going to have a night off booze you might be even more demanding of ensuring you have something great to drink.