To quote Einstein: "Science is a marvelous thing... as long as you don't have to live from it!".
Now let me first say I'm still an undergraduate, and haven't the slightest idea as to how much physicists are paid later on.
I would like to tell you why I think this question is replied as it is here. And first of all, I would like to say it's a very good thing that it is.
The reason for my thinking so is simply this next picture: I have this friend, that any time I say "quantum" or "relativity", or actually anything anywhere near physics, his face takes an expression that's worth seing- kind of like he was sitting in the toilet, minding his own business, when all of a sudden Einstein walk in, wearing only pink socks, and with a full teeth smile asked him weather he could serve him any invariance before dinner, or was he actually light?
For the matter at hand (and because it is, in fact, his real name), let's call him Noam.
Now, I'm picturing Noam, rich, as a Professor of physics. His life would then consist of teaching, researching, and basically dealing with, physics all day long, every day.
In the beginning, sure, he'd suck it up, you know- money and everything (if it was truly enough money).
But soon enough, he'd start hating physics more and more. He'd probably wish, at some point, he hadn't gotten into physics in the first place (which, by the way, he didn't, and all of this is of cours the figment of my wild imagination).
He would rapidly grow very unhappy with his life. But what are you going to do, after years of studying (which in reality, he would never have gotten through anyway), you're deep into it, that's what you've spent your years studying, that's what you are.
I then picture myself, Ph.d. in physics and all, but working at MacDonald's. I see myself still staying on track of things, reading all new research in my field, researching myself (I'm going into mathematical physics, I don't really need funding now, do I?). I see myself happy.
Physics isn't something you should get into if you're not absolutely fascinated by it. Moreover, is you are, indeed, absolutely fascinated by it, you have no choice- you won't be able to live without it, you'll get into it.
So you see, money isn't an issue here. And so, I think the guys' answers here are good in that way that they might "frighten" someone who wouldn't have been happy with physics had he gotten on with it.
Some of you might be thinking that my little story wasn't really needed. Well, sue me.
I would like to express my deepest respect to Albert Einstein, please don't take the pink socks personally.