We are the bride's family. How do we set a fair hantaran without burdening the man's side?

Start with the cost of the celebration you are actually planning, then adjust it to what the man's side can afford. List the real expenses, not figures heard from neighbours or on social media. Ask tactfully about your future son-in-law's means. He will be providing maintenance for your daughter after this, so do not use up his savings before the household even begins. Allah praises those who, when they spend, “are neither extravagant nor miserly, but hold a balance between the two” (Surah al-Furqan 25:67). Leave room for negotiation, and let your daughter have her say too. See family finances.