Perhaps some of you already knew this, but it's new for me. A friend show it to me and I think it's a great resource to take into account when ordering pcbs:
http://pcbshopper.com/
New to me, thanks . Could have saved myself a few quid
I found this way of comparing prices based on size also interesting:
http://www.meatandnetworking.com/resources/cheap-prototype-pcb-comparison/
although the prices here are probably not updated...