I don't think any have been offered money directly for porn, but many have chosen to leak sex tapes of themselves for publicity purposes. Last time I read The Hollywood Reporter, there was an ad from a company soliciting such videos from celebs, offering editing services, pixelation or blurring, and discrete release channels.

I'm not sure which washed-up celeb I'd like to see fuck. Most washed-up female celebs are washed up because nobody wants to fuck them or see them get fucked. Otherwise, they'd still have careers.