For vintage I typically buy from sellers that combine shipping or even give free shipping when you hit threshold. Below is an example. All of these cards had $3 shipping. However, once I bought $35 the shipping was free. Getting 11 Red/Blue Backs that I need for $43 is a great deal IMO. The Billy Johnson Blue Back was the most expensive card, and it is in bad shape, but with these not popping up very often raw and for a decent price, I will buy $6 Blue Backs all day long if they don't have paper loss. So, I like BIN, combined shipping, and quality images.
