Hi Shrimann. This is a very subjective question. The budget for the interior work can only be determined depending on your expectations of the final outcome. Even after that, selection of materials play an important role. The market is flooded with various quality and range of materials. Eg. A tile could range from 30-40 per sft to 200-300 per sft. Now that itself can alter the budget. Sijmilarly, veneers have a wide variety and range.

What would be ideal for you is to identify some materials in the market and then work backwards. Alternatively, you can get an estimnate from an interior designer or a contractor for the work to be done and then fit in your numbers to alter the budget.

As for designer fee, again, that is dependent on the individual's experience and eye for detail. You will find designers who charge around 30-40 per sft and also someone who charges 200-300 per sft. But again, the outcome will be completely different.

At times upfront cost migh sound like a lot, but in long run overall cost, including the saving due to designer's experience and also due to any error or lack of it, might be much less.

It totally depends on what type of design them you want and the amount of details too.

As those thing determine the material and cost of material and the time that will be required to design and build the interior.