One of the things a frugal gardener does is save seeds from year to year. Not only does it save money, each year your seed becomes more and more acclimated to the unique conditions in your garden, so that they become hardier and more reliable.
Saving seeds for most things is fairly straightforward and simple. Let a plant to to seed, pick it off and save it. Here are some radish and onion seeds I have been working on saving. The radish seed here will probably be sprouted this winter rather than planted because the crop was disappointing. I don't want those genes to reproduce, but they do make some fine salad and sandwich material once they've sprouted.
The onion seed (on the paper) are not quite dry enough yet to remove, so I will leave them out for a couple of days. Since onion seeds only last one year and they're not nearly as reliable as onion sets, I'm going to experiment with winter sowing a few, keeping a few just as they are and planting next spring and keeping another few in the garage to bear the freezing temperatures of nature.
We shall see what happens next year!
I have lettuce seed saved already, from an heirloom type that I've had for around four years now. There is still seed from tomatoes, peppers and a few other things. Okra is on a string drying right now.
There are a few things that I've not had good luck saving seeds from, though. Summer squash and sweet peppers never seem to work out. If you know how to do either of those, let me know!