Professor VanBo makes $400 per day, or $2,000 per week, teaching economics at a college in New York. After equilibrating the benefits and costs at the margin, he decides to take three consecutive teaching days off without pay to fly to Atlanta to attend a concert of his favorite band, De Mand and the Shifters. The cost of transportation and lodging for the trip is $2,500. The cost of a concert ticket is $300.

The opportunity cost of the professor's decision to attend the concert is $ ____________.

Please show how you arrived at your answer.