Outrageous prices for not-so great food — the issue of stadium concessions is pretty interesting. So interesting that Slate’s Daniel Engber wondered and found out what it’s like to be a beer vendor. Aside from in airports and on airplanes, where else can you be subjected to a limited number of relatively unappetizing, uncreative, unhealthy concoctions that are sold at unbelievably high prices? Even the July 2006 revamping of RFK Stadium and the new food…