Hello, 

So follwoing link attached will list out the humanities courses offered by IIT Mumbai.

http://www.hss.iitb.ac.in/en/btech

As far as I visited the site, I came to conclusion that they offer BSc Economics in under graduate course in the field you are looking for. rest you can check it out in the site.

Hope this answers your question. 

Hello

Undergraduate Programmes offered by IIT Bombay are

1. B.Tech- Aerospace Engineering
    Chemical Engineering
    Civil Engineering
    Computer Science & Engineering
    Electrical Engineering
    Mechanical Engineering
    Metallurgical Engineering & Materials Science
    Physics
Admission to the B.Tech programmes is done through JEE Advanced exam.

2. Dual Degree- B.Tech + M.Tech dual degree programmes are offered by the institute.
Admission to Dual Degree courses is done on the basis of JEE Advanced exam.

3. Four year B.S. Programme- B.S. Chemistry, B.S. Economics, B.S. Mathematics.
Admission to B.S programmes is through JEE Advanced exam.

4. B.Des programme.
Admission to B.Des programme is done through UCEED exam.

Do let us know if you have any other query.

Good Luck!