Did Cholkar give up sugar because he couldn't afford it? Please clarify the details of his vow and the subsequent actions he took.

This is a slight misinterpretation. Cholkar's financial struggles were the cause of his delay in visiting Shirdi, but not the direct reason he gave up sugar. Chapter 15 clarifies that Cholkar came from a 'poor household' and made a vow to distribute sugar candy if he passed an exam for his job. After he passed, he was unable to immediately travel to Shirdi to fulfill the vow because household expenses were too difficult to overcome. It was during this period of delay that he took a personal vow to avoid sugar 'as an inedible substance,' which was a form of penance or commitment. His giving up sugar was a secret act of devotion related to the delay, not a direct result of being unable to afford sugar itself.