Carver Silver Seven tube amp ad from 1991 (8x10")

Every historical hi-fi or a/v item I triple package is done as follows:
Cello bag, inner envelope, rigid inner envelope and finally an outer envelope.
For display: Cello bag, archival acid free paper backing, and slick back insert.
Two sided items need to display both sides, so I do not use a rigid insert for display.
Ask other sellers how they package and how they justify what they charge for ship & pack.

RIGID envelopes I use vs others soft bendable envelopes:
Sellers who mail you an item of this size for less than $2-$3 are likely mailing in a non rigid envelope
(ask them). Malling an item like this in a soft envelope costs about $.88 to $1.15 (yet others charge $2-$3).
USPS considers a rigid envelope a parcel, not a letter, so the parcel rates apply (click to see USPS rates).
There is also NO tracking for non rigid envelopes.
I use rigid envelopes and about $2 total in materials alone for each shipment.