3,960,000 GP ... using Bob - the Axe merchant in Lumbridge, Tindel - the Tindel merchant at Port Khazard, Dunstan - the Smithy in Burthorpe, or the Squire - in the workshop area of the Void Knight's Outpost.
3,940,200 GP using a player owned workshop.
1,970,100 GP at 99 smithing (wearing...