Well, let me give you a few places.where do you get the beet seed, or mangel? Thinking I might give that a try for winter feed.
Ok, funny that you ask about Mangels I have some seeds and I think I got them at Johnny's under the beet section. However, I have to give you my other favorite places for seeds so you can poke your head in a check it out for beets, etc. I just learned about odd veggies from a class I attended called, "Beyond Tomatoes and Zucchini."
Mangels....Johnny Seeds - larger sizes can be cheaper, but check prices....
http://www.growitalian.com/bulk-seed-for-farmers/?sort=featured&page=3 great service here, and LARGE sizes.
http://www.territorialseed.com/
http://www.italianseedandtool.com/product/BT05/Beet-Yellow-Mangel.html - not tried this one before but it came up when I was looking for bulk for you.
OK that's 4 for you to compare prices. However, there are some seed exchanges and they are FREE!!! I would check your local library and your local Master Gardener's Program. See if they can recommend something. There are actual libraries that carry seed exchanges, how cool is that! These libraries ask you to bring the seeds back next year from your crop. I know it seems impossible, but it's true! BTW, Mangel's are a heritage seed and should be in there!! Oh, side note, they are so HUGE that they work the soil as they grow. Think of it as nature's rototiller! HA!