Is that per person and not including standard gratuities?
If it doesn't include those things, I could do it and have a fairly good time.
I've had on board bills anywhere from $50 to $2000. It all depends on the itinerary, ship, OBC and the number of on board alternative restaurants and the "feeling" of the ship. I've never spent more on liquor than on my, four day, Imagination cruise, last January.
BTW: My wife drank most of it.
I really never "budget" on a cruise but I try to keep it to around $100/day.
If the $200 didn't include gratuities, I think someone could go and have a good time on a seven day cruise for $200.