I’m surprised no one replied to this already, with (at the time of writing) 144 views.
First,when you say “design study” do you mean design research including fieldwork? You also say you don’t need concepts, you want “styling”. So you do want a full design? Because there are no industrial design companies in Hong Kong that actually do research although every single company says it does.
I’d say that the question is too hard to answer. In Hong Kong like anywhere you’ll find a wide range of prices and talent. From the dirt cheap to overpriced, and from very bad design to very professional design; you’ll find every combination, although the talented and cheap is rarest one.