If I do B.Tech from any decent college and M.Tech from an IIT, then what will be my salary package?

The salary doesn't depend on the college. Salary depends on your skills and on your placement. It depends on the company which you got after placement.

If you get placed in government institutions as a professor, the package may vary from 1 lac to 2 lac per month. If you are at a private institution it may vary from 50k to 1 lac or more and there are some more options like if you do PhD then you can go in to the corporate world.