If you garden and you're frugal, surely you've saved at least a few varieties of seeds from year to year. If you haven't, you're wasting money. The seed companies get theirs the exact same way you can get yours, so why pay them to do it?
I keep reading that hybrids won't breed true if you save the seeds from your own crops and that's true of some things, but not all. I have saved seed from hybrid lettuce, radishes and acorn squash, among other things, and they grew true to themselves the next year. It's worth a try, especially if you come across something you really like, or something that grows very well in your garden.
Heirlooms are best for seed saving, though. Think of it this way. Every time you toss out the seeds from an heirloom tomato or a summer squash, you're throwing away a perfectly good package of seeds or in most cases, several packages of seeds.
Nature is extremely generous when it comes to making seed and she will give them to you for free. Why buy them next year?