Hii Sai 

BIT bangalore is a well structured  private university of India. Inorder to take admission in BIT you may apply through various entrance examination like JEE mains, Comedk etc.

As you said you have 75 marks in Mains as well you belong from OBC Category it will depend on the cuttoff of JEE where your rank will lie but apart from the the cuttoff you should also be start preparing for COMEDK examination because colleges in Karnataka like BIT , RV will take most of the applicants via comedk exam. So put JEE mains number behind and be ready for Comedk inorder to take admission in BIT bangalore. 

As you said you are from OBC Category and i don't think so your fee structure will vary from General Category students because BIT is a private college and it doesn't follow the caste procedure for their admission. 

Good luck