Couldn't find anything on whisky, but a according to the central statistics agency a beer would have been about 0.5 euro at the time (i.e. about one guilder). Unfortunately I don't think those are bar prices, which would have been higher.

EDIT: By comparison, a loaf of white bread was 20 euro cents.

http://statline.cbs.nl/StatWeb/publication/?VW=T&DM=SLNL&PA=80345NED&D1=1&D2=150-l&HD=100225-1846&HDR=T&STB=G1&CHARTTYPE=1