Philjb, you can’t include the congestion charge or Dartford crossing in your calculations, if a privately owned car is registered as disabled it’s free anyway.
When I lost my PIP I bought a nearly new car straight away, I knew I would win my appeal so I used the transition money as a deposit drove away the day I handed the old car over. My PIP money now covers the payments and as I got the lower rate of living allowance at appeal as well, that extra cover insurance and other car essentials.
Would I buy a new car again, probably not since I can get what I need on Motability but I haven’t ruled out leasing to get something like an F-Pace or BMW X3 or a future EV not on the scheme.