Does it cost a lot to modify a child support order?

Since you and your "ex" hav agreed to a child support modification by way of stipulation and court order accomplishing such should not be too expensive if you retain a family law attorney to assist you in drafting the papaerwork. I estimate less than $500.

Another option is for you to draft the proposed stipulation to modify the child support order and order and go to a family law attorney for review, your local legal aid clinic, or contact your county bar association to see if there is a program to assist people in your situation for reviuewing documentation for a nominal fee.

It really depends on what is considered "a lot" to your personal budget.  To modify a decree or order, you would need to file a motion to modify.  The exact amount is set by the clerk of the court in your county-- so for an exact figure, call them and find out the filing fee.  Usually, this runs a couple of hundred dollars.  It should be less since you will not need service because "dad" is agreement with the change.  When you ask for the quote from the clerk, tell them that you will not need service because it's agreed to-- this will also reduce your cost.

You will also need a final order on the motion.  Because this is agreed to, the attorney's fees should be much cheaper.  You can shop around, but you'll be looking at a range of $200-1000, just depending on who you get and their billable rate. Insead of hiring an attorney to represent you in the modification, you can try to get one to just draft the motion and order for you-- and then handle the rest yourself.  If you can afford to have an attorney all the way through it's better so that you don't accidentally modify another part of the order that you didn't intend to modify. 

All in all-- you're looking at $500.00-1000.00.  This seems like a lot for some people on a budget, but it is much cheaper than a contested action.  If this still is outside your price range, considering talking to the district clerk to see if there are any legal services or legal clinics in the area that provide free or reduced rate legal services.  As you are lawyer shopping, talk to attorneys who offer payment plans... because of the economy, more are accepting credit cards and payment options to increase business.  A good starting point is the attorney that helped you with the original order.   They may still have a copy of the original order in their computer which will making it quicker and easier to redraft and modify.

You had a couple of related questions-- the first is who pays for the changes.  Often the party who files the motion is responsible for paying the costs up front.  However, it's not unusual in agreed situations for the parties to split costs associated with an agreed divorce or modification. 

Your second related question was regarding the amount.  The court will usually approve agreed orders as long as they don't fall below guidelines.  Meaning, if you were modifying so that he only had to pay a $1 per month, this would be grossly below child support payment guidelines.  Judges can question why you are deviating and increase the amount.  If "dad" is agreeing to an increase which represents a higher amount, the court's usually don't have a rub with it. 

You also asked about him paying more than what is currently in the order.  He is required to pay the amount set out in the order.  However, he can make additional payments at anytime.  So the cheapest option right now would be for him to make extra voluntary payments.  The risk that you run is that later, you will not have an enforceable order if he decides to stop the extra payments later.  You would then have to file a motion to modify-- and if he was no longer agreeable to the change, it would then be much more expensive to get the new order with the increased child support obligation.