"biochar.. soil amendment.. roughly $10 per cubic foot or $250 for a yard"
No name, location or phone number, but it might be someone already on this list. (?)
$10/ft3, assuming a typical density of 220 kg/m3, is around $.73/lb, and $250/yd3 is $.67/lb. Those are reasonable prices.
The only alternative, on this island, appears to be spending around $1/lb on "cowboy charcoal" from a retail store, then taking a hammer to it. I know some folks doing that. I've done it myself. Gets real boring hitting it with a hammer.
The various companies promising high-tech biochar-making machines claim they'll be able to mass-produce and sell at $.25/lb or less, but as that's a ways off, this craiglist person could be a practical source now for those with money.