Who pays for the insurance? If you are paying for health insurance then maybe you should subtract that from your half of the expenses. Health insurance is not cheap I know.
Re. the extra activities.....can you have a say before you agree to half? Some of it could just be normal child support (words from my ex!). I know you would agree to hockey, but trips to Thailand???? I would want to know that child support is going for the children and not just to let your wife live in the lifestyle she has grown accustomed!
