Tupac's sexual fantasies are now another man's treasure because the rapper's hand-drawn love letter to his girlfriend just sold for more than $21k at auction. Tupac's rare prison drawing to his GF received plenty of attention -- and not just because it depicts Tupac and Desiree Smith getting it on doggy style -- earning 10 bids during the Steiner auction. We're told the erotic artwork sold for $21,155.75 ... and the winning bid belongs to a very wealthy man in his 60s. Talk about disposable income! As we reported ... Tupac's NSFW art also included the hand-decorated envelope and love letter he sent to his girl in ... (full story)