That number feels like a punch to the face at first thought.
Labor is a huge part of that though.
This is my build thread....
Re-Rebuilding the 440-493 in a 1970 Charger
It is long and there are many tangents where it goes off topic.
I have yet to itemize everything but I'm around $3000 to $3500 to rebuild the short block. The heads were fine and I reused a known good cam and lifters. I did all the work myself except the machine work.
It isn't just the physical act of rebuilding the engine that takes time. It is everything around it. Saving and cleaning fasteners, brackets and other parts. Properly marking, saving and reinstalling wiring, hoses, sending units, starter-alternator-water pump-fuel pump, etc. Oil, ATF, P/S fluid, anti freeze, A/C recharge if it was disconnected, etc.
They have to add in a measure of $$$ to cover their labor costs in the event of any warranty work as well.
Good luck to you. A fresh engine is a great thing.