Which college is more economical among JMC, Kamala Nehru College and Gargi College for BSc?

Alpine College of Management and technology (Dehradun).

General placements: College has an excellent overall placement data, although branch-specific data is not availed clearly.

Aeronautical (core) placements: Media. Such core aeronautical jobs (aerospace R&D, aircraft design) are not assured by campus placements, like most private colleges.

Jobs available: The majority of Aeronautical students are put in IT, software, operations, manufacturing, QA or a general engineering job, and not necessarily aerospace.

Average package: Placed students will have an average package of about 3-5 LPA.

Best packages: Premium packages sold are typically not routine or general aeronautical functions, but special or exceptional cases.

Recruiters: Firms visiting the campus primarily are firms in IT and service-based business; there are occasional and few references to aviation.

Internships: Alpine aviation ecosystem has some aviation related internships, but it does not guarantee placements.

Reality Check

there are less core jobs in Aeronautical Engineering in India.

It can be required that students have good projects, CAD tools (CATIA/SolidWorks), internships or advanced education (M.Tech / MS) in order to be absorbed into core aerospace firms such as HAL, DRDO, ISRO, Boeing, etc.

Bottom Line
The average placement assistance of the B.Tech Aeronautical Engineering is provided by the Alpine College.
It is acceptable to a general engineering career, but not the best one in case you want to be sure of core aeronautical placements. Campus placements are not the only point. Success is heavily relied on what you can do, internships, and additional specialization.