I think a Powered Penetrating Flame Jet enchantment should be your guide here, since it produces the most similar effect. We'll offset adding the ability to parry by removing the ability to have one per hand.
Code:
Damage Flame Jet Power Penetrating Total
1d $27,200 $16,500 -- $43,700
2d $27,200 $33,000 -- $60,200
4d $27,200 $132,000 -- $159,200
6d (2) $27,200 $528,000 $8,250 $563,450
8d (2) $27,200 $2,112K $8,250 $2,147,450
8d (5) $27,200 $2,112K $82,500 $2,221,700
The fact that you can only access various levels depending on your Magery level is a minor inconvenience of the fact that a Flame Jet enchantment is usable only be mages.