Yes, but the correct thing to do in this situation is to pay the $5,000 for the Hello World program, NOT post it (you never promised to publicize the results), and tell your boss "mea culpa... I tried the programming contest thing and it didn't work out". It wouldn't be the first time that a marketing program spent $5,000 to produce essentially no results... marketing is a very hit-and-miss business at the best of times, so your boss may be annoyed, but should take it in stride.

What you DON'T do is to advertise that you're offering a contest, then fail to pay out the prizes. That's not just sleazy, it's illegal.