I think you can find studios that aren't that pricey. There are old fashioned studios located in many residential districts, often on the 2nd floor of very old buildings without lifts. They don't advertise packages or do any advertising at all, but they do family photos. When you walk along in Central and Sheung Wan or in Kowloon you may see if you find one. You will see boxes with photos at the entrance of those buildings. They cost only several hundreds.
For outdoor shooting, there are many semi-professionals taking salon pictures for young ladies in Hong Kong Park and Kowloon Park on weekends. If you go there you can find them easily. Their prices start from $250 per roll of 36 films. You may find their ads in EasyFinder (sorry it's in Chinese). But you have to ask if they like to take pictures for babies.