Plos one is an open access journal. Most OA journals are charging APC (publication fees). You could ask for some institutional help (some funds) to your publication, or approach the journal editor and ask him if they have a lower fees category for those who need it.
Don't. Just pay. The journals need funding too. You will never regret it in the future and always be proud that your paper was published in a high ranking journal. No one ever regretting paying for something worthwhile, but plenty regret not paying enough and getting junk :)
@Farheen. forget PloS if you cannot pay. You may find journal working on mixed model. Then you choose "subscription" and are free of paying. Other choice: look ad MDPI journals, fee is lower, and some of these can give you full waiver (it depends). Andrew Paul McKenzie Pegman - maybe it is hard for you to imagine, that there are countries where fee is paid by authors only? And PloS fee is 2-3 months salary?
Linas Balciauskas you are right. In India for fresher only Rs 25000 is the salary after doing PhD also. Its very tough to pay PLOS fee but its good rank so I am trying if I get funding.
Andrew Paul McKenzie Pegman thanks for your suggestion. If you have that much amount please fund for my paper. I will put your name on contribution.