In a way, you're completely right that the landlords are scammers..... and in a way, it's completely wrong because it's a reflection of the market value. Yes, you shouldn't have to pay thousands USD for a tiny little dysfunctional space, but the landlord may very well have made quite a sacrifice herself to buy it in the first place. It's an investment and rent is based on demand.
I'm going to go out on a limb -- and sorry I know you didn't ask this at all -- and suggest you maybe don't need to come to "help" your daughter. Is she coming for an exchange semester as an undergraduate? I see students doing this all the time on their own. It's nice to have family visit, but the students do manage very well on their own and, in my opinion, it's a good life learning experience. Hong Kong isn't a scary or dangerous place for a young person, especially if they're with a college/university, and she can have an amazing experience on her own.
Anyway, there's serviced apartments on Peng Chau Island (~30 ferry ride to Central): the harmonium.
And there's wontonmeen | the place we live (But I don't see her advising private rooms anymore).
You won't get a serviced apartment (=temporary apartment) any cheaper, I don't think. And those prices, I think, are fair.