At the Ukrainian National Opera in Kiev.  The opera features the staples of the Russian and European repetoire, along with more unusual works.  Opening night, which we attended, was "Taras Bulba," an opera in Ukrainian which tells the legendary story of a Cossack uprising against the Poles.  We enjoyed it--it's certainly not something we're likely to see anywhere else.  These seats cost about $4.  Even so, about the half the audience consisted of foreign visitors.  Several nights later, on the evening of the performnance, we bought similar tickets for Swan Lake.
 
 

The opera building.