Window A/C Units Average Cost a month? Hi. I live in Maryland, and I just this minute...

Hi. I live in Maryland, and I just this minute moved into a 3 level townhouse that does not hold the duel zone A/C unit. I own the Master Bedroom upstairs, but my roommate and her baby hold the basement. It's lone been a week and we are adjectives already fighting over the heat of the A/C. The other day she have it cranked up to 75 degrees because the underground store gets so cold. My room within turn was boiling. I prefer it cooler, but can matter with thaw rooms, but that was beyond what is comfortable. She doesn't do space heaters, so my lone option immediately is for a window A/C part. I wanted to know if anyone can offer me a ballpark figure on how much that will incorporate to our electric bill? I live in Maryland, so our summers can bring hot and sticky. If she leaves the house set at 75, would our costs go up even more? I know it's complicated to pinpoint the exact cost, but any ballpark figure would be extremely caring.
Answers:    Last time I used one, it cost me about $25 a month.
Ballpark, just about 15 cents an hour x 10 hours = $1.50 a day
$1.50 x 30 days = $45 a month