I never hesitated because of the money. Being poor kind of sucks, but it's more than offset by the fact that you get up and are excited to go to work everyday. It took me five years to do my PhD, at which time I never made more than $24,000, then I spent two years as a post-doc at about $40,000. The great thing about a science PhD, however, is that it's not an expense. The school pretty much always picks up the tab, so at least there's no debt to contend with.
I didn't know that I would basically end up a biologist, but I was reasonably certain from a young age that I wanted to be a scientist. My grandfather worked as an engineer for the Navy and then was a high level administrator at NASA back before it was even called NASA (started as NACA). I always heard his stories about building and testing rockets ("We were literally writing the textbooks," is what he always said), and it made me want to be a physicist. When I finally went to grad school for physics, I went for biophysics, because I serendipitously discovered a love for biology when during a gen ed bio requirement, I came across a book called Full House by Stephen Jay Gould, which is one of my favorite books of all time.
I haven't accomplished nearly what I'd like to, and I hope I don't until I die. I want to keep researching, and making interesting observations. It's what makes me tick. It's frustrating at times, because you can go for months with nothing interesting happening, but then shit like getting your study featured on the cover of the largest cancer publication happens (a work mk and I did together) and it's the greatest feeling in the world (he would never brag about it, but I don't mind ;):
The great thing is that no matter how awesome your discovery, there's always more work to be done.