What you're actually asking is "Would artillery shells be cheaper if we could offshore all the actual work to cast, machine, and fill an artillery shell to China and then just ship the end result over by boat?"
And the answer is yes, China makes their artillery shells cheaper. American labor is very expensive and American military manufacturers tend towards low volume nowadays, because they don't trust the government to commit to 1 million shells a year for two decades, because every time there's a changing of the guard in the whitehouse, plans get gutted seemingly as a "Fuck you" to anyone who worked with the previous admin.
That being said, I'd like to see a citation for the $3k figure being thrown around. The number I've seen is more like $800
"the U.S. currently pays $3,000 for its most modern shells, according to an Army spokesperson. That price includes the charge, fuze, and shell body." [1]
They are big chunks of metal that needs to be identically machined to tight tolerances and filled with explosives and a fuse.
$3k is pretty cheap for custom work.
Then you need to transport and store them.
You can buy drones off the shelf made with cheap components.