Square Cow Card Variety Pack
Pack of six square cards and envelopes, all cows, all the time.
They come with "postage saver" envelopes, which measure 5"x7" but have a glue line to create a perfect pocket for the 5"x5" card. The benefit of this is that you don't have to pay extra postage for a square envelope. (yes, that's a thing... rectangular envelopes cost regular postage, square envelopes are more. It's crazy.)
These packs will ship for a flat $3, whether you buy one or 50.