My state has a set formula that the courts use to figure child support - i.e. 14% of adjusted income for one child, etc.
So check with your state first - do a web search on child support laws in your state, and see if there are any minimum standards as law - you don't want to ask for less than the law would require. Also, before you pay anyone - see if the state provides templates for free.
I found these sites
http://www.isc.idaho.gov/Idaho_ChildSupport_Guidelines.pdf
http://www.courtselfhelp.idaho.gov/
Also, think about a contingency plan is the child's father wants to contest the support - then you may need an attorney. Check with your state or counties legal aide department. Also, some state's Department of Human Services will help with filing.
And don't short change yourself. Research and educate yourself on the laws before making a request. :)
Good luck