Yeah, think someone's not sure what they're doing, so they're pricing it high in anticipation of slow progress.... or just don't want to do it. A headgasket isn't a problem, it's the head that's the problem, IMO. IT needs to be checked to make sure it's flat, as well as the block. Why did it leak in the first place? And with the mileage, it probably needs valve stem guides while you're there, as well as a valve or two... Especially if dusting is a concern. My machine shop usually charges around $600 to RR the head, depending on what's all wrong. Add about $750 for labor here.
The tappet cover is a no brainer, just a PITA. The injection pump, fuel filter, and intake need to come off, after a good washing, then the cover can come off and get a new gasket and back it goes. I've been doing a lot of these this year.... seems the rubber gasket dries out and cracks, leaking out the splits. I don't know what Dodge charges, but I usually charge about $500 if it's really nasty. Takes me 5-6 hrs with a good wash and time to dry.
I've got a guy in Kaufman, TX, that sells reman'd engines for around $3800+core. Install is the mamajama. That's a full day and a half around here, which will come out to another $1500.
I do know I must be a lot cheaper then anywhere else, as I keep 'em lined up in my yard for some reason. And I'm slow, as my mechanic shop only opens when it rains in the summer, and is too cold to work outside in the winter. And still they come. I charge $100hr, and tell people I'm slow, get over it or don't bring it here.