Also the National Center for Charitable Statistics (yes, it exists) provides a decent web interface and data downloads for a wide variety of registered and non-r4egistered orgs. No API that I can see though.
Without being a trained copyright expert, the crux of your endevour lies in your process of aggregating your text corpus:
Over the years, I collected texts from many different internet sources (Blogs, Forums, Amazon, News portals, Project Gutenberg, etc.) by my own, which I aggregated and compiled into various data sets that could be very valuable for the ...
Selected financial information on all entities that file using form 990 with the IRS is public. A variety of datasets can be found in the IRS Statistics of Income (SOI). I would start at this page:
CharityNavigator.org includes a page for every US registered nonprofit. Even if it isn't a rated charity, there is basic data included via a link to the org's Form 990. If the org is large enough (such that it files the full 990), then you'll find those data points on its Form 990.
Citizen Audit is a good alternative to guide star.
The search process is less click hungry.
Getting several fiscal years at a time is possible on a unique page.
More fiscal years available for IRS 990. ( generally go until 2005/2006, where guidestar give, in most case, the last 3 years.
API and bulk access are a possibility ( if ...
As of this posting, the PublicResource.org link doesn't work, the NCCS datasets are also paid, you must apply for OpenCorporate dataset use.
Below is a more detailed list including Activity and NTEE codes from an IRS page found though a Data.gov search:
It's an interesting question. Salaries are the large expenditure. Will the staff be upset if their salaries are public?
I think transparency in a non-profit is essential, especially for charities. If the staff don't want their salaries public, perhaps share the average or median salary as part of an expenditure breakdown.
If you are interested to increase ...