[size=12]It's not so much that one was more common than the other, per se, but that one is an older variation than the other. The one that says "Erie, PA, USA" (or EPU in blue book lingo) on the bottom is a later version than the one that just says "ERIE" with the slant logo.
Speaking on personal experience, I think that you run into the slant/ERIE more often than the slant/EPU, but it's not like either one is particularly rare. I've seen more than one style of handle on the slant/ERIE -- the old-style flattened handle similar to the one that appears on a lot of the Griswold's ERIE and inset-ERIE skillets, and a newer-style thicker handle with a longitudinal apex beneath it like you see on the pans with EPU text on them of either logo. I don't see that so much with the other slant/ERIE pans that I come across; it seems that for whatever reason, they changed handle designs, but then cast a bunch of size 9 skillets before they changed text. I can post photos if my descriptions aren't very clear.
Someone else is going to have to quote you an opinion on fair price, though. I'm not buying right now, so I don't know too much about how prices are running, except that they're too rich for me.[/size]