The NYT had an interesting piece on how many cities are bringing in foreign teachers, under J-1 visas, because US citizens are not willing to work for the pay being offered. This is yet another example of how political power shapes the market and thereby determines the pay in different occupations.
If it were simply an economic question, there would be far more money to be saved by bringing in foreign doctors than foreign teachers. The average pay for doctors in the United States is over $260,000 a year. This is more than twice the average for other wealthy countries. The gap between doctors' pay in the United States and pay in developing countries like the Philippines (the focus of this piece) would be even larger.
If economists actually supported free trade and maximizing efficiency they would be spending a huge amount of time working out arrangements that would allow for foreign doctors to meet US standards and then practice medicine in the United States under the same terms as doctors who were trained here. Unfortunately, the economics profession is more committed to redistributing income upward than to free market principles. (Yes, I am promoting my [free] book Rigged: How Globalization and the Rules of the Modern Economy Were Structured to Make the Rich Richer.)