The 3 inch hulls are usually used for hunting and will carry
a premium price tag.
All small bore shotgun shells like the 16,28 and 410 are in
the high dollar market and can cost twice as much as a 20 or 12 Ga. trap load.
If you shoot the 410 or 28 Ga, you need lots of money for those factory loads, no way around it. It is the cost of owning a "Specialty gun ".

Good luck finding ammo.