Edit car and Track price

Open cars.ini file in your Cars folder using Notepad and make the following modification:

price=10
nfsprice=10

Now, you'll be able to buy all the cars for $10.

Change track price
The edit trick can be done to change the price of the tracks as well. Just open tracks.ini in the Tracks folder and edit all lines starting with 'm_price'. For example:

m_price[0]=10

Change mass of the car
Using notepad open car.ini file located in the folder. For example I.E Cars/911T/Cars.ini. Change Mass to i.e 100 and you will have a rocket Porsche.

NOTE: Before editing, you might need to uncheck read-only attribute from ini files. To do that, browse to the folder where your car.ini files is located, right Click on the file car.ini, select Properties and remove the check from Read-only check box. Also, make backup before editing!