There are too many exchanges these days for new ones to be very effective, you need something a bit more fresh or new in order to make a decent amount of money off of it. If you were getting into Bitcoin during the initial stages and you were able to set up an exchange then, then you would have a lot more potential to earn money and your exchange would be far larger than it is or would be today. You could make a fair amount these days if you have aggressive advertising or you get a lot of people using your exchange primarily, but you'd be looking at nabbing fresh investors in an old market with established exchanges.