Every court has its standard approach when the non custodial parent (NCP) and the child are separated by distance. You can see one approach here:
http://www.divorceinfo.com/standardvisitation.htm#SeparatedByDistance. If the distance causes the NCP's travel costs to increase, the NCP often can ask for a reduction in child support. The CP will often counter, though, that any increase in travel cost needs to be tempered with an adjustment for the CP's spending more time with the child.