A quick check of CA law found the provision you mentioned... 90% must go to the good cause... However, it does not say "gross proceeds" but rather "revenue" and a quick check of the CA legal definition of revenue finds they use the standard definition of "return on investment." So all costs are subtracted and it is very much a "net" requirement.
Here are the gaming regs in a pdf format:
http://oag.ca.gov/sites/all/files/pd..._charities.pdf?
Page 26 has the 90% rule.
I looked because that is an extremely difficult standard to live up to and I know there are commercial fundraisers there and they would not work for 10%.
Also, the State is not intrested in occasional charitable raffles... They make it easier than most states.
art