Since this thread was resurrected, I wanted to comment on this part specifically for religiously-minded homeschoolers considering a CA charter. We use predominantly secular materials, but, as was described above, our charter has been fine with purchasing Rod & Staff Spelling, Behrman House Hebrew, and Memoria Press New American Cursive. I know homeschoolers who have turned in Apologia Science as work samples, and another local charter that actually had Sonlight materials in their resource center for check out. All of this depends wildly on the charter, and I am not sure how some of this is even legal TBH. But, at least in San Diego County, it seems to be less the exception than the rule.
A new charter just opened up here last year that is offering $1800 for K-8 and $2400 for 9-12 per child. I looked at their vendor list, just out of curiosity, and they already included organizations like AOPS and the WTMA among their vendors. So yes, research thoroughly, as that money can make a substantial difference in the lives of many homeschoolers.