Which return you file depends on type of organization and annual revenue. Any public charity can choose to file the long Form 990 even if they qualify for an easier filing. Private Foundations file Form 990-PF. Please query before ordering, 990-PF by quote only. A 990-PF return for private foundations is usually 125-250 pages long!
If annual revenue (gross receipts) is under $50,000, you qualify to file the Form 990-N. Easy, quick. I will give you step-by-step filing instructions for one gig.
If Gross receipts < $200,000 and Total assets < $500,000, you file Form 990-EZ. My fee is a $50 to prepare this tax return and all required schedules.
If your Gross receipts ≥ $200,000, or Total assets ≥ $500,000, you file Form 990. It is almost like filing for 501c3 status all over again (every year!). Many nonprofits pay $1,000 - $3,000 for Form 990 prep. I charge $150. Yes, I know it is less than accountants and attorneys charge, but I don't think it should cost a fortune to file nonprofit tax returns.