I've worked both as a mechanical engineer (on the list) and as a post-doc researcher (one of the most bitched about professions in the comments). As an engineer with just a bachelor's degree, I made pretty decent money, but I didn't care for the work. I then went back to grad school and received a stipend that was a fraction of my engineering salary, spent five years doing that, then 3 years as a post doc. I now make more money than I did as an engineer, but perhaps not as much as I would have made if I had stuck in engineering for the last 7 or 8 years (don't have too much information about the alternate history that involves me not going to grad school).

Anyway, even if I didn't ever get promoted, and I'm making better cash now than I would have otherwise, I still figure that I cost myself more than $200,000 plus interest, so the real value (when factoring in salary increases) is probably much higher.

So the question becomes whether it's worth it. The answer is simple. Yes. It's not possible to put a price on happiness, and I am much happier as a scientist than I ever would've been as an engineer (not that there's anything wrong with engineering; just wasn't for me). I've never starved. I've never wanted for much. So in that sense, I've always made enough money to keep me from suffering (although I would certainly recommend having money over not having it any day, all other things equal).

The post-docs who bitch about how much post docs get paid probably have never held a real job before, and they therefore vastly over-inflate their importance to the world (the old trap of "I work hard and went to a lot of school, so I should get paid in a way that reflects that"...nonsense, really).

When I was in graduate school there was another student who was trying to start a grad student union. He approached me with all the reasons why we're getting royally fucked by the university, the government, society, etc. The only response I gave him was that I went to grad school to be a free man, and joining a union would be the least free thing I could think of. I entered into a contract for a set wage, for a set number of years, and I felt that I was perfectly able minded enough to do so.

The point is that one needs to gather all the information available before making a judgement about what to study, including what their priorities as a person are. If teaching makes you happy, then teach. But don't whine when you make 70% of what your peers make (a. you're still making a living wage, and d. you get a shitload of time off). Finding a career that speaks to you is going to be the best decision that you can make for yourself. Someone is always going to have more money that you. Who gives a shit?