Knowing how much to ask donors for is an art, not a science—but you nonprofit fundraisers already understand that: http://www.wsj.com/articles/the-art-of-suggested-donation-amounts-1481511960?elqTrackId=066ea5a363e04d68968ce8853f344194&elq=3f3f4c4535c448e095e9dc7754e34d4f&elqaid=11798&elqat=1&elqCampaignId=4709