ok... first lets get this out of the way. no orphanages, no nothing like that. Boba Fett is heartless. Read "the Mandalorian Armor". See how he treats his partners and people who thought they were his friends. What I hate is when people write Star Wars books obviously reading all the other books crucial to the character's stories. Some appear to not even have a precursory knowledge of the movies. I liked the Republic Commando game a lot, and like the books a lot too, but in an attempt to point out that clones were just as human as anyone else, they were almost portrayed as weak. So, all this to say, Boba probably spends his money on his massive repair bills. His ship takes a massive beating on a regular basis. For example, when he kills two IG-88s in a row as only Boba could, he completely ruins the Slave 1, even the hyperdrive was not functional anymore. Also, as someone pointed out earlier, He must have lots of medical bills. He takes so many hits, he will do anything do finish a job, and as was also pointed out earlier, he later gets a mechanical leg.
"Some soldiers say that to reach maximum combat efficiency, they need to be in the zone. Sir; I live in the zone." - RC 1207 'Sev' to RC 1138 'Boss'