Why would a desireless saint like Sai Baba ask for money? Wasn't this a contradiction of his spiritual state?

This apparent contradiction is addressed directly in the source material. While a doubt may arise as to why a completely fulfilled saint would need money, Chapter 14 explains that the act of asking for Dakshina was a pretext for teaching. For Sai, to whom pebbles and diamonds were of the same value, the money itself was inconsequential. The true essence of this practice was to teach His devotees crucial virtues, most notably humility. By taking Dakshina, Baba was creating a mechanism for spiritual exchange and instruction, proving that the request for money was not a sign of desire but a tool for the devotee's upliftment.