I haven't checked the tariff list in a while but I don't remember ammos of any kind being imposed.
We collectively need to face the fact that if something is not coming from a 3rd world country then it's expensive. And since China isn't big on shotgun shells, getting them for cheap is gonna be a lot harder than anything produced there.
On a side note though, most birdshot are barely more expensive than the reloading components to make them. Sometimes even cheaper. So I'm not sure what kind of price you guys are expecting, but at some point the price of a finished good can't be much cheaper than the price of the underlying components.