I agree with whomever said if you can't afford the tips don't go, or wait until you can.
It's 10.00 per person/day and is automatically added to your shipboard account. you have to leave your credit card number of a large cash deposit ( minimum 500.00 p/p for a cruise of over 10 days) and then at the end, they either charge your credit card your expenses, or give you back your difference. If you paid cash and your shipboard cash account gets less than 300.00 they won't let you charge anything to the account until you bring it up over that initial amount.
I found that just with alcohol, eating in private dining once, and gratutities and minimal shore excursions, I spent over 400.00 myself in a two week period and I was budgeting.