For SEEED Studio, they make ten boards for a fixed price, and they don't go by size. I suspect if I sent them a huge board it would be different, but I got ten of my TMCC Buffer Boards for around $13, the composite size is very similar to three of these. That being the case, I'd have thirty of these for around $13, not a bad price.
All of my stuff gets panelized at the PCB house, when I get them they're in panels. It greatly increased productivity of the placement of parts as they don't have to do as many board changes to run production. Mine are small runs, for really large runs, the boards can be 18" on a side, they're huge!
Here's a few examples of my stuff when I get it.