Hello Brian,  As someone who makes new discs, I have been shipping
discs for the past six years without any problems (except once when
the UPS truck drove over the box).

My discs are first separated by 0.050" chipboard of the same diameter
as the discs.  Then the discs are placed on a square piece of cardboard
that is much larger than the discs.  The cardboard is cut so that four
corners fold up and are glued in place.  This keeps the discs suspended
from the edges of the box.

This package is then loaded into a flat box I had made for this
purpose.  I realize that most eBay sellers don't ship as much as I do,
but I have found that this suspension package assures the discs arrive
safely.

As Don Caine stated, smaller discs, say, 15-1/2 inches diameter or
smaller, can be shipped safely in pizza boxes but they should be packed
so their edges are not sitting against the edge of the box and the box
edges are completely covered by shipping tape.

I have only purchased smaller discs on eBay and, luckily, they were
packed by someone who knew what they were doing.  Good Luck!

Dave Corkrum
www.polyphonmusic.com