Hello Rahul

SAT exam is conducted to evaluate candidates’ academic knowledge in Reading, Writing and Quantitative Aptitude and other prescribed specialized subjects. 
You will have to pay a registration fee to apply for the exam. 
And, for admission to Universities you will have to pay the University fee. 

However, many Universities also provide scholarship to students. 
You will have to check the criteria of the University where you wish to apply for admission.

Good Luck!