Both 5x10 and 10x10 PCBs are listed as “+$15” in quantities of 10. This seems odd, given you could panelize two 5x10 boards onto a single 10x10 board. Why is this?
Actually, the cost difference for 5x10cm and 10x10cm is small for the small volume. Considering the 10x10cm is most common-use PCB size, we make a special price for it. Wish my answer make sense. 