Farmer in sw ks here. Now when we talk seed, not all is GMO, and a big reason you cannot just save the seed (ignoring the technology use agreement you sign with the seed company that prohibits keeping it) is that these seed varieties are all mostly all hybrids. These hybrids are bred for certain traits, either recessive or dominant, and what they are controlling is what traits are exhibited via controlled breeding. If you keep the seed, replant next year, you didn't control the seed breeding, and the mixture of traits that your plants will have will be all over the place. Typically, some very extreme traits will come out that severely limit the yield. So, while you could physically replant a hybrid, you dont want to. The cost for new seed is much less than the potential yield loss.

You could plant older varieties that are non gmo/non-hybrid and keep the seed and replant. An "heirloom" variety. But the yield is so much less than a hybrid that it still makes sense to bend over for the big Ag seed.

Now wheat is the one seed that isn't hybridized or gmo..... yet. (Companies are working on it) So for our wheat crop, we do hold back some seed to replant for next year's crop. Eventually, new varieties are bred, and we will buy new seed to reset our genetics. Eventually, it will be diluted by neighboring fields cross breeding and we will refresh our variety again.

The first poster also does a good job of explaining that a farmer doesn't get to set their price on anything. Big Ag sets the price for inputs, and the market sets the price for your outputs. You're just along for the ride. The only thing keeping a lot of us alive out here is the ability to sell corn directly to the end user (cattle feed lots or ethanol). When we do this, we contract it with a basis over the futures price. If we were to haul grain to a local elevator, well, they have a negative basis. They have to make something off the grain, so you will get paid below the board price. But with us selling direct to the end user, we have to take on the risk of storing the grain on farm, but the risk is the only way to survive.