Take a look at
Just Host. Hosting plans start at less than $3.45 a month, and they do allow adult websites. Every single hosting feature is unlimited (databases, email accounts, ftp accounts, etc). The domain name is free, for life.
If you use the coupon code "BESTHOST2008", you'll receive another 20% discount ontop of the standard 20%. That's a 40% discount total, for a fast webhost that allows adult content. Sorry, but if you can't pay about $2-3 a month, then I'm asking myself weird questions :p