I am going to go with multiple answers.
1) Fully compartmentalized car account. At least for me, this kind of thing needs it's own pool. All car money, car expense money, repairs, used car sales, and car related tax refunds go into and come out of this 1 car account.
At the rates you are getting paid, I cannot imagine you will ever get close to running out of cash. It will instead explode year after year into an extra retirement account for you.
2) Make a friend with a car merchant. Shopping, also not my past-time. But the amount of money you save by buying used or getting some kind of crazy new car deal is just worth so much money.
For example, we got our current car for $11k new. That added up to ~$14k after tax, tip, registration, tinted glass, etc. We paid cash. It is hard to find a used car for that kind of money. And it is far cheaper than the $450x12x5 = $27k you have available.
3) Passing the car on to your wife is brilliant. That is like a free sale/buy. No tax, no mark ups, nada.
4) Invest aggressively as if for your retirement age long in the future (59 1/2). You have have to money to just buy a car. No need to worry about short term risk, and just end up losing out of longer term gains.