How to Attached Value to Someone's Hospitality?

Recently, a friend has inquired, how much it cost to rent an apartment during the holiday season. You see, I have two mutual friends, one in Indonesia, and one in Singapore. The one in Singapore is going to visit her in-laws in Budapest, Hungary for two weeks. The one in Indonesia, would really like to rent her place while she was away. The friend in Indonesia asked me, what is a fair amount of rent. My friend's condo in Singapore is a 1200 square feet, 3 bedrooms and 2 bathrooms unit located near MRT and only 1 MRT stops from the Central Business District.

These are some number crunches I did:

• Rental value: $5,000/month (for a 2 years lease)
• Utility: $300/month
• Cleaning: $500/month
• Management fee: $400/month
• Service and maintenance: $50/month
• Total: $6,300/month

So I told my friend in Indonesia, the place at cost to the owner is $210/day, therefore offering $250/day will be sufficient. Considering during peak season, hotel charges upward of $300/night, $250 for a 3-bedroom condo is a good deal indeed. In the end, he decided to stay in a hotel around Orchard. He got a good deal of $250/night for his family of four.

The question remains, how do you bring something like this up? In my friend's case, both are aware of the possibility but neither is willing to be the first one to open up the subject. I guess between friends/relatives, it is difficult to quantify the value of hospitality. Undervaluing or overvaluing it can cause strain in the relationship and change it for good.