Herrmann's has a small selection of annuals that are a good price just like everything there.  In the fall I picked up pansys, snapdragons, and flowering kale by the flat.  Also, I have a friend that shops at the Cleburne flea market and buys her flats of annuals there.  I can never remember what day they are open but I think it would be worth the drive.  Seeds never seem to work for me unless I sow them directly in the garden and let Mother Nature take it from there.