I post parcels and letters of all sizes and weights regularly.

Its not just weight - its size as well.

Your record is parcel size, therefore, $7.20, plus packaging, plus ebay postage fees (so postage cost needs to be about $8.50-$9 to cover yourself, unless you want the additional amounts taken from the profit on your item).

To be a large letter size, it would need to be smaller (26cm x 36cm from memory).

Also, Id put some cardboard in there so it doesnt get smashed.... sending a record in a padded bag on its own wont be enough to save it.

The good news about that is that at $7.20 (which is parcel post) it is also tracked, which will help protect you.  Cheaper items e.g. "large letter", are not tracked,, and your item is too big for this anyway.