What about a clunker?

If a car’s private sale value is less than $1,000, it’s unlikely the charity will use it in is work.

It will be sold by or for the charity, at auction or for scrap (at trade-in value or less).
Once you factor in the dealer percentage, the charity will net little (if any) net proceeds from the car.
The charity’s motivation for accepting the car might simply be to strengthen its link with the donor – in effect, the charity will be doing the donor a favor.

$1,000 is the minimum private sale value that will work in the Car Donation Calculator.