Your argument is borderline dishonest. Teachers in Finland don't have to worry about a lot of things U.S. teachers do because they're taken care of by the government via taxes, which results in said utilities and services being cheaper. For example: health care. I also bet that Finland teachers don't have to spend their own money on buying supplies for their students, which is sadly really common here.
Teachers in the US typically have full health benefits paid for by the government as well as a pension and other benefits. So using health care as an example is just inaccurate. Finland teachers also pay a higher tax rate than US teachers so their real income is even lower by comparison. The problem isn't compensation, it's that it's almost impossible to fire a bad teacher and therefore the personal incentive for individual teachers is less than it would be if teachers were paid based on outcomes rather than time in service. Teacher quality is unrelated to seniority. Yet pay scales are almost completely biased towards seniority rather than results. The rules of economics don't end at the schoolhouse door.
Are you claiming that teacher's don't have copays? Because that's patently false. How about before Obamacare when you could be kicked off your insurance roles for having a "pre-existing" condition and then you couldn't find healthcare anywhere? Do you think that didn't effect teachers? People in the U.S. pay more for healthcare than people in Finland do when you take into account the amount of taxes they pay. When the costs of programs are spread among the public, things tend to be cheaper.
Let's take a look at the Finland school system. They have strong unions that are allowed to take an active role in helping decide what's taught. They have seniority. They don't care about standardized tests, which differs dramatically from the U.S. They don't have any No Child Left Behind bullshit.
The students defer drastically, as well. All the students in Finland have healthcare. When they are sick they can go to the doctor and not have to worry about a gigantic bill. They have a poverty rate of 5.3% compared to the U.S. which has a rate of 23.1%. I'm also willing to wager that a significantly larger chunk of their population believes in evolution and global warming compared to the U.S. It's hard to learn when your hungry and sick.
" that it's almost impossible to fire a bad teacher and therefore the personal incentive for individual teachers is less than it would be if teachers were paid based on outcomes rather than time in service"
For what it's worth, it's probably even far harder to fire a teacher hired on a permanent basis in Finland.
http://www.cato.org/blog/no-teachers-finland-are-not-paid-do...
Also, charter schools are public schools. They just have more flexible management and curriculum structures.