In my experience open access is considerably more expensive. Maybe it depends on the field and the journal but places like PLOS often quote something upwards of $3,000 for publishing, and closed-access(?) journals are, ya know, usually free to submit and publish. I could be wrong about that though, and I do know that many open access journals and universities offer price reductions and financial support for cash-strapped scientists. Not only to account for the fact that there's still a strong negative bias towards open-access journals in many scientific communities. A lot of (older) researchers still view open-access as a "pay to publish" sort of deal. I think that'll change over time, and a lot of younger researchers seem much more receptive to open access publishing, but it's hard to convince up and coming researchers to use open access journals if they know that it's going to negatively bias the senior researchers in their field.