how much does a new window cost?

my peace and quiet was quite literally shattered this morning by cw. mw took the two little boys to pick up aw at aunt becky's, where she spent a day, evening, night, and morning being thoroughly and disgustingly spoiled beyond all reason. in exchange for something that i had and he wanted, mw committed to taking all of the kids for the morning. i had grand plans for a jog and a solo excursion to the wax hut. however, cw promised to sit quietly and watch the m's game. no big deal i said. leave him here i said. while upstairs fiddling around, i heard a noise and then wailing. the kind of wailing that emerges from the depths of cw when he has done something that he knows is not good. he met me on the stairs. he threw himself down. "i'm dead meat. that's what i am. dead meat." he repeated this no less than five times. i was rather proud of myself at this point. i calmly asked him, "what has transpired that has you mewing like a dying cat?" he looked up at me. "i have no idea what you're talking about. there is no dying cat down here. i threw the baseball through the window." oh, is that all? he went to his room, grounded from his new mitt and the m's for seven days. a lifetime for a seven year old. or so he told me. i assessed the damage. while playing divers with himself in the living room (not allowed), he threw a major league baseball (basically a stone, carved into a sphere and wrapped in leather) through one pane of the double-paned window. so now what do i do? do i call the rental agency? the last time i called them they charged me $50 to drag an edge of a plastic dixie cup out of the toilet (thank you, aw). i need dave wall to fix this. i half-jokingly asked mw if we could wait to fix it until he comes in october. i mean, it only went through one pane. but it is jagged and nasty looking and i already have visions of a ghost-type impalement in my head. why does this happen to us? what kid throws a baseball through a window from the inside of the house?