Amateurs.
First, the Challenge of the Dragon would be legal. But in recognition of it's danger to the kingdom there would be a fee to be paid: 10% of your worldly wealth (5% for my soldiers), 50% if you are eaten.
THEN I'd go back in time and make a deal with the dragon: "You den in this cave, and I'll start sending peasants into the cave to poke at you with a stick and run away. Do not eat all of them, just the ones dressed as convicts or who smell of a fake "Dragon Repellant" oil. I get to tout the ones you don't eat as people who have proven their bravery...which should bring overly brave fools from all over. You don't have to move to get fed or accumulate treasure."
The Treasure will be accumulated from the estates of this who failed.
I will also strongly encourage my political rivals to try this out, offering a 1% fee...and some "Dragon Repellant."