Went to Monsters, beautiful store, drove there from Brooklyn, worth the time and traffic, picked up some Amano Shrimps $3.00 each. Then went to Fish Town USA, picked up 18 cardinal tetras $1.00 each, and some loaches were on sale polka dot botias. Out of 18 cardinals by next morning just 4 servived, polka dot loaches developed ich in my quarantine tank. Now on treatment. All alive. I did not expect to pick up sick fish from Fish Town USA.
Cardinals are wild caught and always have a chance of getting a super stressed batch. I have had problems like that to. They get moved so much before they land in the store. Usually the trip to a new place does them in. Same experience I've had.
Why don't you just call Petco and ask when they'll be on sale. They may know or be able to give you a better idea than we can. But I don't think it will be for $1. I don't think I've ever seen them for sale anywhere for $1.