Making your own seed mixes from the local seed store works great. I hunt on a camp in Alabama where the owner is a friend of mine's father in-law. In exchange for hunting there we help he take care of the property in the offseason. That includes helping him plant the food plots. We disc and prepare the soil and he plants his own seed mix that he creates from seed he buys at the local seed store, the same one the local farmers use. He mixes things like rape, brassicas, rye, oats, winter peas and turnips for our green fields. In addition he plants okra and quite a bit of corn. The green fields this year turned out great, we got just the right amount of rain after planting them in the fall.
I'm grateful for having learned a lot from helping out. Someday if I get some property of my own I'll plant the food plots the same way, it's a lot more affordable and works just as good, in my opinion better in most cases. We've actually bought Deer blends from Walmart and Bass Pro to plant and compare to the seed from the local seed store. In most cases the local seed store grows thicker and greener than the Deer blends bought in the store. Give it a try and I'm sure you won't be disappointed. Make sure you fertilize and lime if it's necessary.