We went - boat to Sylhet. (Fill in the blanks with appropriate preposition)

The phrasal verb "cut down on" means to reduce the amount or frequency of something. In the given sentence, Luna has reduced the amount of her budget, which is a common way to express financial control or austerity.

    
• Cut down on: To reduce the amount or frequency of something.
    
• Example: "We need to cut down on our expenses."

Other related phrasal verbs with "cut" include:

    
• Cut off: To separate or discontinue. (e.g., "The power was cut off.")
    
• Cut out: To remove or stop doing something. (e.g., "He decided to cut out junk food from his diet.")
    
• Cut back on: Similar to "cut down on," meaning to reduce. (e.g., "The company had to cut back on staff.")

Therefore, "down on" is the most appropriate preposition to convey the meaning of reducing a budget.