I don't know why you would put how much a person makes together with how big their collection is. As some have already pointed out, living expenses play a huge roll in that as well as time. I say time as I've been collecting since '85 and my collection is huge. (4,000 plus)

I've spent a great number of years building it up as my income/expenses have changed (both up and down) over all those years. I mean, yeah, money play a big factor in how big a collection can get, but a little money over time works just as well as a large amount can quickly.