It seems the $300 average spend is due to most nonprofits never really getting their accounts started and their campaigns set up in a way that would actually get their ads to show. Sad.
What kind of quality scores to you see on your keywords? Not all of them will shine, but do you have a healthy number of them performing at 7+? Do you have keyword-driven landing pages? Do you track conversions?
If you like, you can get in touch and I'd be glad to take a look at your account for some ideas. We're not an agency, but we have great Adwords intelligence in our team, and have been helping others make better use of Google's generous offer. We max out our Grantspro account every month, so we know a thing or two about getting the word out with Adwords. ;-)