Soul Society: Where does the money come from?

So, I was thinking...

Obviously, it takes money to form and run an organization like the Gotei 13. And it's been up and running for over a thousand years!

But, where do they get the money to fund things like repairs and the officer's paychecks? It's not like the Gotei 13 was built for profit. And where did the Head Captain get the money to start it!?