You need to decide what you want to do, first. You will make money, regardless of what you do. If cost is the only factor than I would suggest you to stay from further studies. If you really want to do cost analysis do it over 10 years, 15 years and 20 years. You will make more money as a full time professor than working in the industry.
If you like teaching than only go for PHD.  
Everything depends on what you want to do. If you are not sure take some time off and think about it, talk with your professors and professionals in the industry before going either way.
Good luck.