dotNET

No. C is a core programming language. Its a procedural programming language. It gives you a basic knowledge about the programming language. You can pursue C certification Course but OOP (Object Oriented Programming) language has more demand than Procedural Programming language.

Kindly visit the link mentioned below:
http://www.slideshare.net/mir_majid_kant/dotnet-basics
This will give an idea of how much basic knowledge is required to be a .net developer.

All three languages are very good. But, if you want more package compare to other 2, then you should learn Java because android is also based on Java. But, Java is little hard compare to other. .Net is also a very good choice.
If you are near from Pune then PHP is also very good because there are so many domestic company which work on PHP in Pune.

The fee structure varies from location to location, city to city and institute to institute.
If you are based in India, then NIIT may be the right choice. It charges around 8,000 to 44,000 rupees for .Net depending on the duration of the course.
You may choose the duration of the course according to your needs. If you are doing a Computer engineering course, then even a short term course will be fine as you must be familiar with basics of programming.
The duration scope of a course can also be decided as per the market demand. If you want to become a core programmer, then opt for a detailed curriculum course.

I think Java and networking have better scope in future.
1) For many years Java language is providing the best technology solution to the industry and also it is the most secured platform.
Also, you can see that Java is the core technology for android. Android also has a good scope in the current scenario.
2) Networking is one of the best fields because we have to do something new to get better and secure mode of communication. Also, after CCNA, you can clear CCDA.

If you are planning to be an application developer, you must do courses on both Oracle and .NET.

Yes . Computer Science can be learned by anyone and certifications are available for even a kid.

.NET alone is not going to work. Stll you can expect a min of 30 K per month