Travel for academic purposes is now a lot easier. Instead of lining up a substitute, you can simply assign a lecture or two or three from the Mises Institute's YouTube Channel, FEE, or EconTalk (among many others). My Mises U lecture from 2009 covers a comparative advantage example that students and instructors might find useful, and my favorite EconTalk podcast is still Mike Munger's 2007 discussion of recycling. Probably the most useful video I've seen is Roger Garrison's lecture on the Austrian Theory of the Business Cycle, which I've used in my economic history class and which I will probably use in other upper-level courses in the future.