A couple of things:
I don't know about other states, but I do know that in FL, there is a state law that prohibits a dealer from giving any discount on an extended warranty. I think that explains why, if you do a Quick Quote on the Ziegler site, and choose FL in the dropdown box, the quote will come up only showing normal retail price for the plan. If you choose a different state in that dropdown, then the quote comes up showing retail price (crossed out) and the discounted price.
That may explain why the OP in this thread got such a high quote from Ziegler.
I bought my '09 1500 in GA (I lived in FL at the time) and the dealer told me right up front he would sell me whatever warranty I wanted, at $100 over cost. I got the Lifetime MaxCare on my '09 for $1600. And I dang sure got my money's worth out of that!
I bought my '19 in MD and the dealer offered me the MaxCare and started at sticker price. I immediately asked "you know I can buy that online, right?" From there, he asked if I would be willing to buy it from him from $100 over cost and I said sure. It was all very easy and pleasant.
Buying it through the dealer, I had the option to pay in full. But, he also offered me something he said they call RapidRemit. I paid 10% down on the warranty (and a maintenance plan) and pay the rest over 12 months, with 0 interest. A totally separate thing than the actual loan for the truck. I didn't want to finance it in with the truck, but I also didn't really want to throw down that much more cash out of pocket right then, either, so the 12 months/0 interest really worked out well for me.
Anyway, unless you live in FL, there is no reason you can't or shouldn't buy an extended warranty from the dealer. You just have to do your due diligence and know what you should be expecting to pay before you even walk into the dealership.