Rulers tended to get creative when they had no money. In the Alexiad it's written that when Alexius deposes the reigning Emperor they don't bother closing the treasury vault because it's empty. To alleviate this he had to request the Eastern Orthodox Church to fund the various early wars of his reign. People were scraping gold off of the roofs of churches and doors along with any silver and gold objects the Church used day to day. Later on he would have tax revenue after various reforms but that early period was dicey. There was no large banking institutions until after the Crusader period, most loans would have been done on a personal level between nobility.