I don't buy that much seed these days. I save my own, swap with others and belong to a couple of seed circles and the Heritage Seed Library.
I look at a few sites including Real Seeds, Seeds of Italy, D.T. Brown and Baker Creek in the US for new things and things that are difficult to save or don't last but only buy 2 or 3 packets a year.
Our allotment site isn't big enough to make a collective order worthwhile.