Lots of excellent advice so far.

I 100% agree with knowing insurance costs *before* you buy a car is critical. At 16 your biggest expenses will be insurance and maintenance. The differences in insurance rates can be huge from one car to the next (Supra vs Corolla, for example). Some car brands like the european ones will have higher insurance rates because replacement parts are a lot more expensive than parts of Asian or domestic cars. Repairing a crashed Audi or BMW will cost more than repairing a crashed Toyota or Chevy.

If you are looking at used modded cars, be careful with the ones that have had extensive engine or drivetrain work. Not everyone who mods cars knows what they're doing and you could end up buying someone's nightmare. Buying a car that has had just wheels and stereo stuff added isn't too bad as long as the drivetrain is still mostly stock.

Lastly don't forget to budget some $$ for repairs and maintenance once you buy the car (unless its practically new). Almost no one sells a car that needs nothing. People get rid of cars because the cost to fix or maintain them is too much. The new car will likely need a major servicing (oil, trans, coolant flush, all new filters, etc) and some new parts like tires or brakes. Even little shit like taillight bulbs and new wiper blades will prolly be needed. Getting caught up on maintenance can cost anywhere from a few hundred to a few grand so budget accordingly.