Quão rico é Sirius Black?

Uma "quantia razoável de ouro" quando comparado com o de Harry (mas presumivelmente menos) mais tudo dentro do Largo Grimmauld.

Sirius deixou Harry com sua própria fortuna e posses pessoais,

"But first of all I must tell you that Sirius’s will was discovered a week ago and that he left you everything he owned. (...) This is, in the main, fairly straightforward,” Dumbledore went on. “You add a reasonable amount of gold to your account at Gringotts, and you inherit all of Sirius’s personal possessions."
_{(Harry Potter and the Half-Blood Prince - Chapter 3)}

A quantia razoável de ouro provavelmente veio de sua herança de seu tio Alphard, sendo que Sirius foi preso desde os 21 anos.

Yeah, I camped out at your dad’s during the school holidays, and then when I was seventeen I got a place of my own, my Uncle Alphard had left me a decent bit of gold — he’s been wiped off here too, that’s probably why — anyway, after that I looked after myself. I was always welcome at Mr. and Mrs. Potter’s for Sunday lunch, though.”
_{(Harry Potter and the Order of the Phoenix - Chapter 6)}

Sabemos que Sirius comprou uma moto e uma vassoura de fogo, então a herança não estava completamente intacta quando ele a deixou para Harry.

A única posse de nota que Sirius tinha era Buckbeak.

There is also the matter of the hippogriff, Buckbeak. Hagrid has been looking after him since Sirius died, but Buckbeak is yours now, so if you would prefer to make different arrangements —
_{(Harry Potter and the Half-Blood Prince - Chapter 3)}

Sirius também deixou a casa e a escrava de Harry, a Família Negra.

"The slightly problematic part of the legacy (...) is that Sirius also left you number twelve, Grimmauld Place. (...) Black family tradition decreed that the house was handed down the direct line, to the next male with the name of ‘Black.’ Sirius was the very last of the line as his younger brother, Regulus, predeceased him and both were childless. (...) if you have indeed inherited the house, you have also inherited —” He flicked his wand for a fifth time, (...) “Kreacher.”
_{(Harry Potter and the Half-Blood Prince - Chapter 3)}

Note que a casa e tudo nela valem muito .

“Sirius?” said Mundungus, who did not appear to have paid any attention to this conversation, but had been minutely examining an empty goblet. “This solid silver, mate?”
“Yes,” said Sirius, surveying it with distaste. “Finest fifteenth-century goblin-wrought silver, embossed with the Black family crest.”
_{(Harry Potter and the Order of the Phoenix - Chapter 5)}

Ele não deixou a fortuna de Harry, a Família Negra, como ele nunca herdou, tendo sido escrito fora de sua herança. A casa era uma exceção. A julgar pelo valor da casa, se ele tivesse herdado sua fortuna também, sua riqueza teria facilmente diminuído a de Harry.

G.James estava certo que Sirius recebeu a herança de seu tio. E de acordo com a citação abaixo Sirius ficou muito rico.

Sirius's uncleAlphard, Walburga's brother, sympathised with his young nephew and left him a large inheritance, most likely causing Walburga to blast Alphard's name off, as well. Sirius was left financially independent by his uncle’s generous bequest.

Em referência ao que Sirius deixou Harry, não consigo encontrar um valor monetário, parte de uma história de fan fiction. O que Harry recebeu de Sirius foi

• A casa da família Black e todos os seus conteúdos
• moto Sirius
• Kreacher
• O restante do dinheiro dos Alphards, bem como o restante da fortuna da família Black
Buckbeak