if he's just dragging his heels, and not actually refusing to pay up, tell him you need your money back now. send him a text saying you'll be over tomorrow to pick it up and set a time. if he doesn't have it on him, tell him you'll give him a week and then you will look at your legal rights. make it clear that he has YOUR money, YOU did him a favour but now YOU need it yourself. say it like you mean it!
it's a bit vague but I don't see you as the type to go for a heavy-handed approach.
best of luck :o)