Am I justified in my frustration?

I’m right there with ya Rusty. To me a rebuildable core would include a good ring and pinion not rusted to ****. See the first pick. My big error was taking someone for their word because they’re in a reputable Mopar club and he’s a member on this forum. Figured he would care about reputation and representation of his club.
In the back and forth emails we shared he started listing prices of all the individual parts of an 8.75 rearend saying I should be happy I got such a good deal. Axles-$100. Yeah, if I don’t have to damage one pulling the damn thing out. Third member -$350. Okay, if I could get it off and the thing isn’t too heavily pitted on the machined surfaces. Backing plates - $50. Yes, they’re there and they might just end up being the only salvageable part.
He thinks I should feel lucky to have got such a “good” deal. I’ve got quite a few hours labor in this thing and have only got one axle freed. I’ve got $25 dollars worth of WD in it. About to have $23 worth of PB in it. I thought the ring and pinion is good to use from a rebuildable core but that’ll have to be another $150.
Most of this guys posts on here is For Sale ads. I’d be suspicious of anything this guys selling now.

I guess he figures all your labor for blasting it apart with dynamite and cleaning everything up is worth nothing. Oh well.