for 3 years car was without registration ? where it was hiding ? a penalty for non registration starts 90 days of Customs declaration / clearance date stamp.
it will cost you approx 150000 ~ 200000 + penalty if you are a tax payer & have a NTN, incase you do not have national tax number within 12 months after registration of vehicle you will receive notice from FBR for declaration of income sources.
read this & do some maths