Where to buy cells and flats?

I just finished building a large light table for germinating tomatoes and other garden plants. I want to germinate and grow seedlings in the plastic, 6 cell packs, 3" deep that fit standard 1020 propagation flats. I think there would be either 48 or 76 cells per flat. I've located a few suppliers on the internet, but many of the suppliers price the flats and 6 pack cells like they are made of gold foil instead of plastic.

Since I have never germinated seed, I have no idea which suppliers of materials are good. Any suggestions?

Ted