If you have to clear a backlog in your subject, you need to pay Rs 6000/- per subject whether you take it in the summer sem or opt it in the next semester. Although if you wait in the summer sem, you will also have to pay extra for the hostel and mess.

But it may be an extra burden to clear 3 more subjects along with your next semester's subjects. If you wish, you can clear the subjects one by one if you can handle extra subjects but make sure that they are not prerequisites for some other future course. Although I would suggest that since you have three backlogs, you can wait in the summer semester itself because clearing them in the future semesters (with 27 maximum credits), you may have lot of credits to be completed in the last 2 semesters which may become problematic during the placement season.