How much money should I take to Vegas?

Staying at the Bellagio and I have no idea how much money I will need to take with me. I'm not really much of a gambler and I looked at the prices for "O" and nearly fainted. I am going with four other people (siblings/cousins) and I want to treat them to something nice - but not so extravagant that I'll put myself in the poor house. Any recommendations?