The rules governing party law vary from state to state.  Most just require getting the signatures together to send to the state board of elections.  Having people go collect those signatures will obviously need either volunteers or money to pay people to do that.  Of course after the party has been created meetings will need to be set up to create the political party charter, a website will need to be made, candidates will need to be fielded and their campaigns supported, etc.  The actually founding probably doesnt need much money at all besides the paper and pens to collect the signatures.
 
Where to get the money to run the party and what are the rules governing where and how you can collect funds is another tricky question.