As almost everywhere prices have increased significantly over the years and trackside vendors seem to charge whatever they feel they can get away with. However, in 2014 they have probably overdone it a little, reportedly despite a record number of visitors the queues were much shorter than in previous years.
The following prices have been reported from the 2014 race by CA members:
Prices for standard stuff like beer, burger & fries did not vary much, since many of the food stalls seem to be operated by the same company. Looking at these figures it becomes obvious that bringing your own food & drinks to the track is a big cost saver. But don't forget that glass bottles are not allowed on the premises, so bring your drinks in cans or plastic bottles.