Ask HN: What kind of prize would get you to enter an online contest?

What type of expected value would you need to have to bother? For example, For 1 minute I would need to have an expected value of at least $1 (where EV = probability to win * prize value)

would you rather have a higher chance to win a smaller prize (like a technical book) or a smaller chance to win a bigger prize (like a macbook air)? Assume the same expected value

What are some examples of prizes that you would want to win?