The sad fact is, local interpreters, like teachers and instructional aides and various other school district employees, are paid fairly for what they do compared with the national averages for those positions. $18 an hour is a living wage, and is competitive with what similar positions pay in other US school districts. Portland-area interpreters are paid slightly more, corresponding to the increased cost of living, while many other Oregon interpreters are paid less. 

I wish someone would pay me handsomely to write fiction, which is something I find rewarding and also a job that offers great freedom and flexibility. Unfortunately, the market says I should do something else if I want a decent standard of living, so that's what I do. Maybe some of these interpreters should follow suit. Meanwhile, they get PERS, have summers off, and get to work with kids instead of dealing with office politics. There are pros and cons to every line of work.