(I asked this a year ago but didn't get any traction, trying again because I am extremely curious and I have been unable to find anything online.)
In his work published in 1957 on the European Reformation, Will Durant wrote that Queen Isabella of Spain originally rejected Columbus’s request for support of his attempted journey to Asia across the Pacific, until a baptized Jew who advised her told her it would be a good opportunity to convert many people to Christianity. This person then organized a loan that financed a large portion, possibly a majority, of the journey that eventually led to Columbus landing on San Salvador. How accurate is this portrayal viewed by historian’s today?
Here is the relevant text: "At this critical juncture a baptized Jew prodded the march of history. Luis de Santander, finance minister to Ferdinand, reproached Isabella for lack of imagination and enterprise, tempted her with the prospect of converting Asia to Christianity, and proposed to finance the expedition himself with the aid of his friends. Several other Jews- Don Isaac Abrabanel, Juan Cabrero, Abraham Seniorsupported his plea. Isabella was moved, and offered to pledge her jewels to raise the needed sum. Santander judged this unnecessary; he borrowed 1,400,000 maravedis from the fraternity of which he was treasurer; he added 350,000 out of his own pocket; and Columbus somehow got together 250,000 more. On April 17, 1492, the King signed the requisite papers. Then or later he gave Columbus a letter to the Khan of Cathay; it was China, not India, that Columbus hoped to reach, and which to the end of his life he thought he had found. On August 3 the Santa Maria (his flagship), the Pinta, and the Nina sailed from Palos with eighty-eight men, and provisions for a year."
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.457.975&rep=rep1&type=pdf
In a way, yes. Luis de Santángel, not Santander as Durant has it, served as the comptroller-general for the Aragonese crown under king Ferdinand. He was the grandson on a converted Jew and, as a converted Jew serving the court, he and his family were exempt from the scrutiny of the Holy Office of the Inquisition by the king. While it is unknown whether or not this was the norm for all conversos in royal service, it is known that Ferdinand did grand this exemption for the Santángel family since Luis's brother and son also subsequently served the Aragonese crown as comptroller-general. While historical studies of where the funds for Columbus's voyages across the Atlantic are not very numerous, those that do touch upon it are bound to mention Santángel in some capacity. It seems that Durant's source of information for the other Jewish sources of funding is Cecil J. Roth's Jewish Contribution to Civilization (1945). Roth seems to confirm Durant's writings. However it is difficult to determine where Roth's information came from since he offers his sources but does not indicate which pieces of information came from which source. Something important that Durant seems to have left out from Roth's writings is that some of the names given were those of conversos also in royal service.
I have no reason to doubt these claims, but the thing that neither of these writers get at, which is the most interesting part at least for me, is the motivation behind their provision of funds. Of course after Columbus's landfall in the Caribbean, the motivation becomes quite clear in wanting to fund Spanish colonization of lands in the Western Hemisphere in which crypto-Jews may settle and practice Judaism under less scrutiny. Some have proposed this as the motivation behind Santángel's and other conversos' provision of funds, but the motivation before the first voyage remains what appears on the surface as Roth put it: to increase the prestige and power of the Spanish kingdoms of Castile and Aragon by finding new trade routes to Asia.