No, you cannot secure a MBBS seat free of cost at any institution. You will need to pay the decided amount of fees for the course at any institution.
This is almost impossible until you score 720 marks. The only difference will be in the fee structure of the college.

• For Government College :-
  

The fee structure will be lower (in thousands), hence, saves your money.

• For Private College :-
  

You cannot predict the fee structure of a private college, as they are decided by different colleges as per their requirements and policies. They maybe as high as 15 lakhs per year.