A Pam Anderson nude photo shoot doesn't come cheap -- TMZ has learned Playboy offered Pam a cool $25,000 for her upcoming pictorial ... and she's turning every penny over to charity.
In fact, Pam never even accepted the check -- she had Playboy send the cash directly to Waves 4 Water ... a charity that distributes water filters to people who don't have access to clean drinking water.
Anderson tells us, "Waves 4 water are my heroes. They get things done ... and yes, Playboy wrote them a check when I shot the cover (Jan. 2011 issue) directly for 25Gs."
Pam adds, "I've also donated personally. I wish I could do more. Indonesia, Haiti and Pakistan are all in need of these filters. Spread the word!"