Offer 15K to the first person willing to accept that price for the lettered Firestarter-no bullshit just money, or the seller of a complete matching set of The Plant for 6K. Make the offer good for 96 hours. The first to accept gets your money.
Stand firm. (Prices are not going up).
If by chance both items are being sold by the same person-offer 20K, take it or leave it.
The strongest position a buyer has is being able to pay promptly, know the market price(s) , and be firm and willing to walk away.
There may be only 25 asbestos Firestarters in the world, but at this time there are at least two sellers-and perhaps only one buyer.