There's a lot of inflated numbers in this thread.
$30k minimum for a single/couple in HK?! That's over the top. Maybe for an expat who can't stomach the thought of living outside of the Mid Levels and downsizing (accept it, you're not getting a 5 bedroom detached house in Hong Kong for European prices!), but most (non-expat) people spend a fraction of that.
Many many locals have incomes less than $20k, some even $10k, and consider $10-20k for an apartment plenty.
You should have absolutely no problem finding a nice, sufficient (for a single/couple) place on Hong Kong Island less than 30 minutes commute to Central for $10-20k. The closer to $20k, the newer the building and the bigger the area (at $10k you're looking at around 500sqft on HK Island which is a bit tiny, but not abnormal in HK). Look around Causeway Bay, North Point, Quarry Bay, etc, they're all affordable in that range (also try Tin Hau & Tai Koo, a bit pricier but nice areas and easily affordable on a $15-$20k budget).
If you're moving from London, expect to pay basically around the same in Hong Kong, except you'll get less than half the space. But that's how things are in HK. You can't expect exactly the same apartment space if you're getting paid basically the same. A 3-5 bedroom detached house on the outskirts of London is pretty normal and affordable for normal people, the same thing in Hong Kong (unless you're looking at a really old building, far out on a NT Island) is reserved exclusively for overpaid expat bankers and multi-millionaires. Just forget about making the comparison and you won't mind so much.
On the plus side, shops open past 6pm, public transport works, everywhere's within 10-30 minutes commute, and you won't get knived for looking at a teenager 'funny', so that goes some way to compensating for the cramped living space.