Should someone excited about research but who really wants to earn lots of money do a PhD? I'm asking on behalf of a friend.

He currently holds a temporary position at one of the top research institutes in the country. I know that he is excited about his work because he talks enthusiastically about it all the time. He'd ramble on happily for hours about the developments in his field and how the work done at his institute has a very real effect on society. 

However, he has recently been offered a place to study for a PhD at the same institute. Though a great opportunity he is rather worried about the financial cut he would have to suffer if he takes up the offer. 

Given all the stuff that's around on the net about how you should not do a PhD if money is really important to you, I'm wondering what a person in his position should do (i.e. loves research, but really wants to earn money) and what I should say to help him make a decision. 

For what it's worth I'm a PhD student too (studying a different field at a different university)
You shouldn't do a Ph.D. if you don't love research.  You also shouldn't do a Ph.D. if you want to get rich now, since it will require a number of years living on a graduate student stipend.

However, most STEM field Ph.D. graduates have ample opportunities to make lots of money, including:


Founding a startup based on technology developed during their Ph.D., or joining somebody else's startup
Selling out, particularly if they have a solid mathematical background: there are any number of hedge funds and such that are desperately hunting for magic dust to give them an edge.
Just about any industry job will pay a well-suited Ph.D. well - not enough to make you rich, but enough to live a very comfortable life-style.


Of course, there is the danger that by the time one finishes a Ph.D., they may have become twisted such that they are no longer quite so interested in money per se, as happens to many of us.