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.

Sure, hiring is expensive, but firing is really expensive! I salute your efforts to get it right on the first try.