Nobody has mentioned clothes peg nipple clamps?! For shame
They're the easiest DIY toy around. I suppose there's not much creativity involved, though.
I keep meaning to get round to making a flogger out of an old pair of the boys jeans. Just slash the material at regular intervals, leaving a few inches of solid material, then wrap it round (whilst gluing) some thick dowel. Easy peasy. I've also been tempted to get some electrical tape to weave a whip or flogger, as well.
Also got up to a bit of jiggery pokery with a female chastity belt to make it suitable for males. Couple of ways to make it work, but probably difficult to describe without diagrams.