Assuming you are dealt 100 hands per hour, your average bet is $25, and you play for 4 hours, your total action is 100 hands x $25 per hand x 4 hours = $10000. In your 4 hours of play you've given the casino $10000 worth of action.
Casinos use the following formula to calculate how much of a player's action they expect to win:
Action x Casino Advantage = Player's Theoretical Loss
I will go conservative and say Mirage would probably assume they have a 1% edge over your action.
$10000 x 1% = $100 expected loss
Mirage should roughly give you back 30% of your expected loss back in comps.
You would have earned $30 in comps in 4 hours.
24 hours over your trip is $180 worth of comps.
Now in this case that could cover a weekday room at Mirage. The thing about MGM/Mirage is that they are very easy to get discretionary comps. Ask for a food comp after every blackjack session. They should easily write you a $30 food credit. Every time I have asked for a food comp they have given me one!