Gateway Greening has seed packets of flowers and vegetables for sale for only 25 cents per package. The main reason they are so cheap is that they are last years seeds. Some may even be older, so they probably won’t germinate as well as fresh seeds.
I’ve been told they are only for sale on Saturdays from 9 a.m. to noon, but since no one is there to take your money, you may be able to get seeds most of the day. You put your money in a box in the seeds area. It’s run on the honor system.
They keep the seeds in the “Carriage House” which is just up the street from the Gardens and they are on the second floor.
As of today, March 5th, they still have a good selection.
Note – this is only a St. Louis thing, you may be able to find another group like this in your city.