money from the dad??

So baby daddy and I aren't together, in fact he lives in a different state. Anyway, he has been very supportive throughout my pregnancy and we are trying to figure out logistics of everything before the baby comes. Yesterday he asked me how much money per month I want him to pay, and I had no idea what to say! This is my first child and I know they are expensive, but if anyone has any advise on an actual dollar amount that would be very helpful. Thanks!!