When you think of power, your engine come first in mind. Increasing power is one way to accelerate faster and have a higher top speed. Modifying your engine can be cheap at first (ECU, CAI, etc) which are just a few hundred dollars. However if you want to take it a step further, and have forced induction, these mods come with a hefty price tag (Turbocharger, Supercharger, etc). When modifying your engine, make sure your car can handle the extra power it will be making (crank case, differentials, tires) and upgrading your brakes might be a smart decision.
When modifying the body of your car, it brings personality and ownership to the car. There are many cheap kits online to modify the exterior of your car. However these sometimes look terrible. That’s why it is worth it to save up and buy a wider body kit or customize it by a body shop.
Modifying your exhaust might be something you want to do. Not only can you gain quite abit of power by doing so, your car will also have a nice unique sound.
Tire, suspension and brake mods should probably be one of the first mods you do on your car. Modifying these items will make your car handle better and be safer. Although some may think that these upgrades are a waste of money, I personally think that these mods are even more important than body mods and are cheaper than some engine mods.