Plan to do give away every month for top 3
Who make the best prediction
And profit the most
This how I think to attract winners.
Later on they we may hire them and pay them more.
Or allow them to add donation on their profile/subscription.
Will see how will it play out.
This is a good start and I am sure that you will add more gimmicks from time to time to ensure that many people are going to visit and interact on your blog because some might find monthly contests boring not unless if the prize that we are talking about here are huge of course but I like the idea of hiring your best predictor.
You will pay them but I am sure that you will also find a way on how you can earn more money. You can use those top predictors in your betting service. It must be a premium one of course. To have a donation box is I think not really effective because there will be users who will only hit and run or also called as leechers.