I had sees this before, but somehow, I didn't realize it at first.
remember I sayd long time ago, that the two parts of the car code defined, the fist half the logo and name of the car, and the second part the car itself. C63D48AAC63D48AA
What I didn't realize then, was that the first hald of the code, also determines if the car is locked or not, aswell as the cars price!
So if you cahnge the first half for, for example the generic police/traffic car code AF2DC3C1, you will have the car unlocked in the car lot, even if you just started the game, and costing 0$. (Notice that now the car code will look like AF2DC3C1C63D48AA)
This works for any car. Have fun.