Marks and Spencer has a variety of different types of mince pies each year that are approximately between HK$50 to HK$60 a box and currently have a buy one get one offer, so a pretty good deal for some tasty pies. They even have a gluten free version for those that are looking. I bought two boxes for the price of one here.
Feather & Bone is a great store, but I was surprised they were selling Mr Kipling mince pies for HK$88 a box.
Oliver's The Delicatessen has also Mr Kipling mince pies (deep fill) for just HK$23 a box, which I would say is the best deal that I have found and decided to get myself a box.
Pret A Manger offer individual mince pies for HK$15 each, which is great if you just fancy having one and not planning to buy a box of them.
In addition you can order some mince pie bites from Tai Tai Pie Pies online or they may have some (not sure) at their counter at Great in Pacific Place. Check out their website HERE.