It may make you feel a little better to know that the list price for a month's worth of Singulair is $135 so $25 actually isn't too bad.
Right now Singulair's patent runs through 2012 but Teva Pharmaceuticals is trying to introduce a generic version later this year - Teva and Merck (which owns the Singulair patent) have been fighting over Singulair in court and no final decision on the case has been announced.
There's nothing cheaper out there yet but something could be coming soon if Teva wins the court case.