Hey,
There is no need to go for any coaching Institute to get good rank in PG. It's a myth that coaching centres will help you get through any entrance exam.Coaching Institutes just provide you with reading materials and previous year question papers but ultimately everything boils down to your hard work and dedication.Trust me!Your poor financial condition cannot stop you from achieving your  ultimate goal if your approach is correct.
Make sure you are investing time in self study which matters the most. Be thorough with the syllabus of your undergraduate course. Utilise the library of your college or outside. Look up contents online. Make notes of all the extra details that you are learning.Keep yourself abreast with the changes in the pattern of the exams etcetera.Solve previous year papers of the respective entrance exams.And most importantly,have faith in yourself.
Good luck.

Hello, don't worry about your economic background there are various sources to learn let me tell you
1. You can get standard text books present in your college library using them you first refer the concepts clearly and understand them.
2. If you face any problems with text book you just goto YouTube there you can have various lectures on each topic
3. After learning concepts write free mock tests online and the more you become better.