If you pay this time, you'd better be prepared to keep paying because you can expect a bill from your ex and his friends each time he takes your daughter.
It sometimes happens that an absent parent is the 'good time Dad' (because this is usually a father, although not always) while the person with primary custody has to be the disciplinarian, but expecting the ex to fund Dad being the 'fun one' while being unable to fund interesting outings herself because all the spare cash has gone to the ex is appalling.
In other words, DO NOT PAY. And yes, I'm yelling because I'm so disgusted at both your ex and his friend. Unless your custody agreement says differently (and if you aren't Halle Berry in disguise, I doubt it), you have no obligation to fund activities when your daughter is with her father.