Unless you are a mutiple return customer you most likely are not going receive any discount on a 2019 because they are either already spoken for by the customer that ordered it or if is is a stock allocation the dealer knows he an get full price for it. As far as the 18s unless the build is a complete dog it will still fetch full price fam some putchaser.
Anywhere from 0-$3k off depending on location and relationships. There are a ton of leftover 2017s sold as "used", but never sold to a customer, for $15k off. Of course they've depreciated about that much so your savings will mostly disappear when you sell it on.