RH:
Saving seed is a special circumstance we will talk about, but first I will tell you that the only "heirloom" I care much for is the Brandywine tomato. That one I like, but I also like the new ones--better boy, early girl, porter, etc.
When it comes to saving seed, you have to consider how many varieties of any one crop you plant. For example, if you plant zucchini, yellow crookneck and patty pan squash in the same garden you will not have any seed worth saving--they WILL cross and you will get some speckled, odd shaped squash not worth having. Same with tomatos, peppers, just about any plant that pollinates. You can save potatos--they are propagated vegetatively and are not going to cross. Don't expect to save seed from a straight 8 cucumber if you also grow a pickler. The new varieties of sweet corn or so much better than the old open pollinated kind that it is a waste of time to save seed.
If all you want are open-pollinated varieties, and if you are willing to grow only one variety of each crop you can save seed very well, but you can't plant pinto and kentucky wonder beans close together and expect to have good seed.
All that said, the seed companies go to great pains to bring you good seed, true to variety and high-producing. If money is an object, save seeds from crops where you grow only one variety. For the rest of them find a bulk dealer and buy your seeds by the dipperful for fifty cents per dipper. There are a couple of such places in Tulsa, at least two in Muskogee. I'm sure there are some in Claremore, too.
Ox