If you worry about lowballers, you shouldnt be selling cars or anything else for that matter. You do have a good idea though, but not just a under 1k section. Split the Auto for sale into price brakets:

$1500 or less
$1501 - $3000
$3001 - $5000
$5001 - $10k
$10k +


That would GREATLY help people that are trying to stick to a budget.