Tourist visa to Hongkong in Bangkok

You can apply for HK entry permit in Bangkok. The required documents are as follows: the application form with a recent bareheaded color photo glued, your passport and copy of its data page, proof of financial support such as your bank savings account, transportation arrangement such as flight itinerary, and your travel plan to HK as well as your Non-B entry permit to Thailand. Afterwards, submit your application to the embassy of PRC.

Then how much do I need for my bank savings account, I mean the minimum?

There is no exact limit for the amount of money you should have, but I think it should be at least enough for your travel in HK.