The brass knuckles method would be the expensive route to go. It would be 8,301 for each hand for a +1 Shock Brass Knuckles for at total of 16,602 gp.
Since Flurry of Blows allows the monk to attack as if he had the two weapon fighting feat, it would require the monk to attack with a second weapon, instead of striking twice with a single weapon. Hence, needing brass knuckles for each hand.
Since the monk already does lethal damage with his hands, and the damage amount is taken as the higher amount that the monk's hands do, the only advantageous set of brass knuckles, for a monk, is a silver or adamantine set that is used to bypass DR. For other classes, they have a little more use, but the cestus still beats brass knuckles.
For a monk, the preferred weapon is the Amulet of Mighty Fists. A +0 Shock Amulet of Mighty Fists would cost 5,000 gp to have both fists attack with the Shock property. With this route, you are sacrificing the +1 enchantment to attack and damage, but gaining the +3.5 average elemental damage. At 20,000 gp, you can do +0 Cold & Shock or +1 Shock. The amulet is the one exceptional "weapon-like" item that does not require a +1 enchantment before adding special weapon abilities. And shock is better than flaming, because you are less likely to set a flame someone's scroll that will eventually become loot.
I will take a look at the character in just a bit.
