No. Not reasonable.
The electric fee for a full charge 85 KWH, assuming 80-90% efficiency may be less than HK$ 150.
Also, according to HK Law, re-selling electricity is not legal.
I've thought about either
1) the carpark management can instal a "public" charger for everyone in the building / estate, lets say from HKEV power, so everyone can charge their cars if they have, and charge accordingly.
2) allow you to instal a separate electric meter for your own private charger , so you can pay the Power company directly. ( They may like to charge you higher management fee ).
Installation fee of HK$ 4K is not expensive but the monthly charge is too high.