I paid $56 one way to Kona on my flight on the 10th... and I spoke with a few other passengers on my 98% full flight -- no one within earshot got the $19 fare -- most of the passengers paid $43 and I think one person paid $39.

When I booked my seat a few weeks ago, I can only assume that more people paid more - so if go! is getting an average of $50 a seat, at 49 seats, thats about $2300 bucks (take out the 7.5% fed tax) for a 40 minute flight... which is above the cost of a CRJ for that flight.