The leather is typically a fairly cheap material to obtain. Mostly, due how common it actually may be compared to the number of skinned goods used for crafting. Older leathers are also fairly cheap for the most part. Just depends on which transmog sets players are after at the time.
While accidentally posting a few stacks of heavy leather on the Auction House for 5k each. To my surprise, they actually sold. Hearing from others, they are able to sell this material for up to 60g per unit! Unsure of which transmog is causing such a large influx of prices for such an old skin. If you know, you could possibly be making bank from this material.
There will be more locations to farm heavy leather, but for now, just enjoy the few that have gone over. Never had a motive to push heavy leather locations out until now. A playlist will also be uploaded as soon as I can get enough videos out to make it a worthy playlist.