This term was used in a TV show recently and was referring to the price of another highly prized liquor by saying it was worth 3 or 4 stacks of whiskey. The show was a recent episode of NCIS Los Angeles. In very last scene they sat down to a toast with Hettie.
I believe they're referring to stacks of boxes. Now, seeing as how bottles of whiskey can vary widely in price and stacks of boxes can be of any height, the phrase doesn't really mean anything at all. My conjecture is that, if it is a fictional series, this is one of the many instances in which a line sounds cool enough that no viewers catch on to the fact that it means nothing. You can see this all the time when science or technology terms are thrown around on tv.
Just for fun let's make some assumptions. If a stack is 6 boxes high and you use something cheap like cases of Jim Beam two or three stacks would be between 2150 and 3240 dollars. That's a pretty wide range of numbers but not an unheard of price for a bottle of liquor.
You can keep the expensive bottle though, I'll be hiding in the corner with my 200 bottles of whiskey.
According to the urban dictionary web site, a stack is a G or $1,000.00 US dollars. This makes sense since the price of a bottle of Yamazaki 2013 Sherry Cask is $3,999.99 in 2017. cfb
I watched the episode of NCIS LA S8/19 and it makes sense. The reference meaning the bottle of whiskey they were drinking a Yamasaki 2013 Sherry Cask was worth 3 or 4 stacks ( $3000 -$4000). Cost $3999 in 2017