hi ashish
Before screen based trading, it was very easy to write a software for stock trading. Now with so many regulatory compliance issues and accountability and low brokerages and high volumes, the smallesst back office software will easily have a few lakhs of lines of code. It is much more easier to buy a package. They are normally priced segmentwise approximately 50000 to 1.5lakhs per segment per year. They maintain the code and incorporate regulatory changes automatically and allows you to concentrate on the business.