The prizes (Maui trip, second/third prizes, swag kits, shipping for the swag kits) probably cost around $20k in total.

Assuming an engineer costs $200k/year, 200 effective working days per year, that's 1k/day. Developing the contest (from the idea to building the rules to building the site to playtesting) likely cost more than 20 eng-days, making it the biggest cost.

Hiring is expensive. If it takes 30 minutes to screen one candidate for suitability for the "real" interview and 5h to do a "real" interview (including evaluation etc.), 5 screenings for one interview-worthy candidate and 5 interviews for one hire (I suspect the real factors might be closer to 10), that's 12.5h of screening and 25h of interviewing per hire.