[Calchet]

I'd personally do something like add an additional "Get stuck in!" bonus weapon to orcs, usable once/battle, to represent their opening bonus - that way, it can be fine-tuned for power with more precision than slapping 'charge' on their regular choppas.

On the topic of costs, my plan for the enslaved version is to have
Choppa Boyz at a cost of 10/5 or so, Big'uns around 14/4, Arrer Boyz around 10/7, Gobbos at 6/2 or thereabouts, and Black Orcs much higher, perhaps 19/15. For other greenskins not enslaved, Snotlings at 3/1 for a six-pack should be about right by my reckoning, letting twelve be had for the cost of a gobbo.