I have had good luck with these.
They are not designed for soldering directly to wires, but you can if you are careful. They are also a bit flimsy unless you encapsulate them with epoxy or hot glue and heat shrink. But they are cheap, they do not require a custom crimping tool, you can cut them to any length, and they can produce a robust custom connector if you take some care. I also think that using them encourages students to improve soldering and assembly skills.
http://search.digikey.com/us/en/prod...7034-ND/810173