How much would this day be in Bangkok, Thailand?

First off your in China Town a travel jam in itself so you may forget about a 9 minute ride maybe 20 would be closer depending on traffic. A tuk tuk is not the way I would want to take my grandma around Bangkok, the heat, humidity, and fumes is not enjoyable. I would say about 60 to 80 baht for taxi depending on the traffic. You can get lunch at any stand for 30 to 40 baht if you want to eat Thai, western food figure 100 to 200 baht for lunch. Try going to the Grand Place, Wat Po and Khao San Road.