Cruises!

My boyfriend and I want to go on a cruise for our 21st birthday in December (he’s 2 days older). I’m just wondering how much money we should expect to spend as I’ve never been on a cruise. I found a 7 night cruise for $500. If I bring another $500, would that be enough for activities? Is that a reasonable amount of spending money? I could do $1000. This is just for me alone. His expenses are separate.