I love love love Grahtoe Studio's forks, but they are not exactly cheap. I will let someone else recommend cheap forks for you.
My favourite easy updo for forks is the Lazy Wrap Bun. Watch the video to see how she makes the bun, but then go to 1:00 and pause it. You see the first loop on the right hand side of the bun? I twist the bun so that loop is pointing upwards. Then I take my fork and insert the tines partway down that loop, and through the stem part of the bun (where the hair comes up from your scalp). I then try to catch a little bit of the end of the second loop on the way down, and I hide the tines in the hair on my scalp below the bun. It takes about 15 seconds once you've got it figured out, from gathering the hair into a pony, creating the bun, and inserting the fork. It is very stable, I've been wearing this all day while gardening.
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