Hey, the folks at DonorsChoose.org do something like microfinance for classroom projects.
They define a project, put it online, and people fund in small amounts to get bigger results.
Check out Completed: Learning in Motion- Physics Day at Six Flags!, just funded:
"I am an inclusion special education teacher for 8th graders at a dynamic, successful neighborhood school with a diverse and primarily low-income population."…How can we thank you enough for helping to make this fun, educational, and engaging experience available to all our students? Well, for one, we can ensure that this field trip will be meaningful and memorable, and will do our best to inspire some of our students to continue their studies in science. Who knows- perhaps a future NASA scientist, Ford engineer, or Nobel Prize winner is among us, waiting for the seed to be planted! In addition, we will be sure to document the results of your generosity through photos and student reflections about what this experience meant to our students. Check back with us after May 6th!