My expectation is that she will get an offer and I will too. So when we go on our cruise in October (not a comped cruise) I plan on dropping $800 on the slots because that will be less than a balcony stateroom would cost us if we paid full price. So my wife gambled $300 or so (as far as she's telling me) but the amount of money she gambled could've been $500 or more overall depending on how much she won and lost along the way.
As you play you win a little, lose a little etc. This isn't an accurate number but for demonstration purposes let's say every $100 you win back on average 90% of it. I watched youtube videos of people discussing this and they said slot machines have a certain payback percentage on average.
So, you get a point for every $5 you put into a slot machine. All I know is that after my wife gambled around $300-$400 dollars she was getting offers for cruises after we got back.