It'd be awesome if more people made money out of fanfics.
Do you know how many people on DeviantArt earn cash from drawing characters from games/books/etc as commissions for fans? Take the computer game Dragon Age: Origins as an example. Fans will approach an artist and might say, "I want a picture of my character Princess Cousland with King Alistair. Princess looks like...etc etc" and the artist, for a modest fee, will draw it, slap an 'Alistair is copyright of Bioware' disclaimer on it, and send it to the fan. Artist gets money, fan gets picture of Princess CousCous and her King, Bioware gets props.
I don't know about the legalities of this, nor of fanfiction. Like I said, it'd be awesome if more people made money out of fanfics (some do), but it's not something that I am personally interested in going for, mostly because the idea makes me uncomfortable. Other people can go for it, and good for them if they get somewhere.
But have *some* integrity, for the love of God. At least acknowledge where the inspiration came from. Don't pretend it was all yours if it wasn't. Most people won't care if you're making money out of something, so long as your methods aren't underhanded or cloaked with deceit.
Not many people like liars.