Diploma

If you do not want to do B.Tech then you can go to BE or if not then you can go for BCA since you have done the Diploma in CS only or you can look for a job. But there are very less jobs and the scope is also not satisfactory. If you have any choice for the undergraduate programme and have a query regarding that please revert.

There are many good colleges in Pune, basically, the government colleges like College of Engineering, Pune etc.
Here is a link:
https://www.shiksha.com/b-tech/ranking/top-engineering-colleges-in-Pune/44-2-0-174-0

It depends on the college in which you are going to take admission. In private college, the fee is more as compared to a government college. In UPTU, the fess is about INR 96000 for private and 60-80K for the government college. In Punjab, the fee is about 85000 INR in both private and government colleges.

Since you are already BE in CSE, therefore CCC certificate is not required for you to apply for government jobs. You can apply to government jobs directly. CCC certificate is required for those who doesn't have basic knowledge of computers or want to get a job in networking.

Hello Yashraj,
It's great to know your desire to do graduation after Diploma and that too in Pune. This city is considered as a cradle for good education. There are plenty of good colleges. I am attaching a link that I hope will help you in coming to a considered decision.
https://googleweblight.com/i?u=https://www.shiksha.com/b-tech/ranking/top-engineering-colleges-in-pune/44-2-0-174-0&hl=en-IN&grqid=M0RUexxB

Top Aeronautical Engineering colleges in Mumbai (All) are mentioned in the link provided below. The ranking is based on engineering ranking 2015 published by The Week.
https://www.shiksha.com/b-tech/ranking/top-aeronautical-engineering-colleges-in-mumbai-all/49-2-0-10224-0