A little light for groom and bright
There are so many nice ideas and glasses for tea light holders. Thus, you have the choice between all possible kinds of colours and shapes to make a creative and beautiful money gift for the wedding.
Buy an angular tea light holder out of glass and a fitting tea light, perhaps even with a nice fragrance. Out of wire you can build a great framework and fix a red paper heart to it with a cute wedding saying written across or just A little light for groom and bright. With a paper-clip you can attach the bill(s) folded to a square or rolled up.
Very creative and effective, but discreet!