here is the deal. You stated that you have an expenses of 750 for a 501(c) set up cost.
If the organizers did it themselves, the filing fees with the state would have been way less: Please see the list of fees here: http://www.sos.mo.gov/forms/corp/cfeesch.pdf
You would have had a registered agent, I assume. Most likely one of he ones on this list: http://www.sos.mo.gov/business/corporations/registered_agents.asp
Most charge a fee to act as your registered agent.. So if you have a registered agent that could go as high as 750 but that would be very high. A typical registered agent may charge only 100 to 200 dollar plus state fees. If monthly it could be between 25 and 50 dollars a month.
750 dollars is a magic number. That number is XXXXX what a company charges to do the work for you. (between 500 and 750 dollars) Most charge 750 dollars.
The thing is, who ever is doing your accounting should know who this bill comes from. You are not indicating who it comes from. I get the idea from your question, you might not know that. But lets assume you do know or can find out.
If the source of the set up fees is from a third party provider, then they likely have receivables policy of payment on account of : demand, 30 day pay, 60 day pay, etc.
It is possible to contact this person and ask them for installment payments based on your status as a startup non-profit. I can not speak to the source you have, but most would work with you.
NOTE: if you had incorporated yourself, any fees to the state would have been paid when the forms were submitted. So unless the 750 is from a 3d party provider, I doubt it is a state source.