after googling a bit it really looks like a D80 would offer you a lot more actuations without letting you down, I'd find this important considering you're buying used, of course they'll all take wonderful pictures, but still, 150$ is not supposed to be too much of a difference,for something better built,and maybe better in a lot more aspects. I also remember somebody suggesting to always buy something newer, as there still is a lot of developing in this department.
so,I say D80,if the money is really a problem,D70s,which the second one considering new tech,right?