To get unlimited money in franchise mode, after you enter the Walmart NASCAR name, go to "Edit Driver", then press B to back out. It will add more money.
In the "Edit Driver" screen, enter your first name as Walmart (case-sensitive) and last name as NASCAR (also case-sensitive). Then, press Start or highlight "Done" to exit the screen. Every time you go back to the "Edit Driver" screen and leave the first and last name the same as you first entered it, and you exit this screen as done previously, you will receive another $10,000,000.
You can unlock Dale Earnhardt Sr.'s Thunder Plate for free by simply having him as your favorite driver on the main menu. You can then change your driver again and the plate will still be available.