I plan to study in Hong Kong. Is it expensive to rent a house in Hong Kong? How much is two rooms and one living room per month?

You can't rent two rooms and one living room at Luohu for 3,000 Hong Kong dollars.

They're all here for soy sauce,

For HKU, it will cost 7,000 ~ 9,000 RMB a month on Hong Kong Island for 30 years, and the new 10000 RMB or more.

Dali is a big city, similar to HKU, and houses in Kowloon are not cheap. There will be 6000~7000 Tang buildings in Mong Kok, but you can calculate the two rooms and one living room of more than 30 square meters.

It's cheaper in the New Territories. Those who live in Sheung Shui and Shenzhen are ok, 4000~5000 a month.

You can Google "Studying in Kaiya, Hong Kong", a local study institution in Hong Kong, where you can search for free information. It is more reliable than reading these pure passing information here.