MtGox, the largest exchange, charges less than 0.60%
The volume that we are expecting is nothing in comparison to the volume that mtgox gets. Add to it the cost of setting up and running a MSB in India and the costs shoot up dramatically. With people charging 10-20% over mtgox rates in India, a commission anywhere near the 5% mark should come as a relief to many.
People advertise with mtgox + 10% but hardly anyone buys with those rates except the newbies.
Most of them offer to pay the rates based on btc-e.
Secondly, make sure you do your homework. buysellbitco.in is one of the guys to reachout to. he has been here for a while and had his share of troubles.
With the advantage that i have (dual citizenship of USA and INDIA), I also worked for a few months to start a legit exchange with its offices in both USA and India, spent money on lawyers and attorneys and finally on the verge of giving it up. Setting up the USA part is easy, but RBI rules and so rigid that there is hardly any allowance to squeeze something like bitcoin.
Word of advise : (1) do your homework on how your exchange should work (2) spend lots of time with your lawyers going through all the test cases. (3) make sure your platform is rock solid and hacker safe. (Pls note, anyone who understands how crypto currency works is himself a script kiddie hacker.)
(4) If you need help or get struck, reach out to the community.. there are some really nice people out here and we will definitely help you out.