Anya has to be the only woman in the world to get the equivalent of a hard-on from reading Walt Disney's comics. A good thing too. Otherwise she'd have sold Xander's childhood treasures on ebay long ago. It's the image of Uncle Scrooge taking a swim in his money that turns her on, just like the smell of fresh banknotes makes her hot.
One day Xander draws out all their money, even borrows some more from colleagues and friends, and they make love on a bed of crisp ten-dollar bills.
Later she tells him it was her best birthday ever.