I follow my DD's lead on these. I lay out that this is the opportunity, this is the commitment, and these are the opportunity costs (because obviously spending 450 minutes a week swimming means 450 minutes you can't be doing other activities, and when you factor in preparation and transportation times, the cost is even larger). If my DD is willing to make that commitment, I'm willing to support her.
Inevitably, whenever my DD has an activity that takes up this much of her time, she starts to growl about it, and we end up scaling back.
