By the pound would be fair, given dry wood. “Fair” prices and wood are hard to match up. A little extra moisture in the wood adds weight and therefore profit, but makes the wood less valuable. If you go by volume, you end up with a BTU mismatch. A combo of quality standards, honest dealers, and easy measurements is needed.
To start with, clean dry wood chunks at 20% moisture or less, sold by the pound and bring your own bags?
As for a base price, try and figure how much time you’ve invested in it, and set some sort of value based on that. Big chunkers at a sawmill make cheap wood, hand split chunks are more expensive.
Gasoline price equivalent is around 20 cents/pound, or $3 for a 15lb bag.