Interesting idea. Aren't you afraid that it would attract qualified candidates who are just interested in earning easy $500 with no intentions of actually getting the job?
It is just an idea, but the idea is that you would only pay out after the interview process. If you actually get good people applying then your job would be to try and attract them to come and work with you. Sure some would just be in it for the money, but as long as you attract some serious people then it would be worth it.