No need - if you share any of the 15 free fundraisers on social media that you are allotted each year, you will receive a free additional fundraiser! IE - share it on Facebook/Twitter, and you get another free fundraiser...so you should never run out! 

If you absolutely insist on paying for more fundraisers beyond your free 5 each year, (no social media, private operation, etc) they are available for $25 each in your manager dashboard.