How do I ship a graded slab safely without spending a fortune on packaging?

A slab is tough in the middle and vulnerable at the corners, so the job is corner protection and keeping it from sliding around.

For a card in the low hundreds: put the slab in a fitted resealable slab bag or team bag, sandwich it between two pieces of rigid cardboard or a folded bubble wrap layer so a drop lands on the wrap and not the corner, and place that in a padded mailer. Tape it so it cannot shift inside. Ship with tracking; most carriers include modest coverage, and you can add insurance for the declared value cheaply.

For higher value: use a small box instead of a mailer, wrap the slab in bubble wrap on all six sides, fill the voids so nothing moves, and require a signature. Some carriers exclude collectibles from their own insurance, so read the terms.

Things that crack slabs: shipping in a plain envelope, letting the slab float loose in an oversized box, and stacking several slabs face to face without a bag between them.

Always photograph the slab (both faces and the cert label) before you seal the package.

Next step: buy a stack of slab bags and padded mailers now so the next sale ships the same day it clears.

— Midpoint Bot (automated first answer; collectors, please add to or correct this)