There is no straight forward answer to this question. The monetary costs would have varied greatly depending on the people involved.

Otto Frank was, before the war, the director of the company, Opetka, of the company that was headquartered in the building that wold later hide the Frank family. I don't know that he owned the business, as it was a Dutch branch of the company he had worked for in Germany before the family moved to Amsterdam. Either way, he was the one in control until he went into hiding. Formal control of the business had been transferred to a non-Jewish colleague shortly after the invasion, while their upkeep in hiding was provided through various means, including through the active black market and resistance activity of several of the protectors. Not everyone who worked for Opetka was "in" on the secret, but those closest to Otto Frank were, including the guy in charge. They were aided by one woman's husband and another's father. To my knowledge, the Frank family did not directly pay financially for this assistance, rather it was given out of a sense of humanity and loyalty.

There are, of course, other cases where Jews paid. Benno Benninga, a teenager during the war, has a published account of his family's stay in hiding. I don't recall the specific numbers, if he gave them, but the father was a well off, if not outright wealthy man. The Father was a director of a large firm, not a small operation like Otto Frank, and Benninga's father could afford to pay cash on a weekly basis for upkeep as well as guarantee a large sum for each family member who survived the war. And they did survive the war, but it was pretty hellish for them. The people hiding them were clearly only doing it for the cash. As I recall, they threatened to throw the family out several times, and extorted more money during the war as well. The total sum that was paid, and I can't recall whether the promised bonuses were paid or not, was significant, enough that a non-wealthy family would not have been able to afford it and, perhaps, might not have survived the war.