Cost of interior designing

Hello ,

I have just zeroed in on a duplex flat (in Bangalore) I want to buy. The deal wud be done mostly by may end or june. The house already has cupboards done in the bedrooms and kitchen.

I am looking for a designer who can help me with the living room and dining hall designs. Also, i wud like to have a small pooja mandir done too. Besides this, there are other work like curtain holders in all the rooms and modification of the cupboard which is already present ,under the staircase .

I would like to know how much would all this cost approximately.

I have certain ideas in mind but would need help from a professional hand for effective utilisation of space and reduce clutter.

Also, we are anyway going to whitewash the house once before we occupy it too.