A quick Google search on false rape allegations :
http://www.icdv.idaho.gov/conference/handouts/False-Allegations.pdf
This study shows between 2%-10% of allegations are false. Sooo, just going off the high end percentage, if 30 women have come forward stating Cosby raped them, that means that 3 of them may be lying.
The victim-blaming and "they are lying for money" is rather disturbing, particularly when it comes from other women. Personally, you could not pay me enough money to come forward with false accusations of rape, especially against a celebrity. Public humiliation and people calling me a liar? Nope, I would pass. (which is why I think there are probably MANY more victims we will never know about)