I've never had much luck straightening shoot shafts by hand. It seems like I just chase the bends for days. I create 2 bends for every one that gets straightened. I found the idea for this arrow straightening tool during a random search, so I don't know the source. It's a sapling approx. 2 inches in diameter with a 1/2 inch hole drilled at about a 60 degree angle through it.
I don't know how to explain it that well via typing, but you want to drill low enough on the sapling that it doesn't break through the top of the hole. Then you trim the material away from the top of the hole creating a channel with a small lip on the top of it. This keeps the shaft in place while manipulating.
Then, I use a knife to clean up the two edges that the shaft will contact when pressure is applied. This makes for nice smooth contact surfaces that won't dent, kink, or break the shaft. This little tool is a life-saver! It works really well.
Hopefully the pictures can give you a better idea of what I'm trying to explain. So far, our expenses are $7 folding saw, $9 survival knife, a couple bucks in fuel for the drive to the site, some free shoots, and a free sapling arrow straightener. The saw and knife will last for hundreds of shafts... possibly indefinitely, so I'd say we're on track for a low-budget build!