First If you don't have a saw mill and want a timber then you will throw the extra boarding and price / bf out the window, that is not the goal, the timber is and how do you achieve that by the simplest means, I should say lowest cost? You already have the timber, no cost there. No cash outlay.
The second is along Marks lay lines, I would have to add the cost of the log into the equation though. The butt end of the log would fetch a higher price so why use it as a timber at all. So, you would have to be brave and stick $1.00/bf to it, there is $208 before you even start. Hewing may take some practice but I don't see you having to pay $25, I would put $10-15 on it, I will go the low road=$160 for a cost of $368. Now feed the horse, I round the total to $400. I don't buy hard wood timber does anyone know the going price for ash timber?
In addition why even hew it after it is sawn? Doing that has always.. not done much for me. You can tell when it was sawn and then hewn, there is that extra bit of perfection that doesn't quite make it actual.
You would only be adding to the cost of the timber by hewing it after it was sawn. Why would you do that? It would cost more in the end.
I would not saw a 25' timber exchanged for the edgings. Flat grain, sappy, short, tapered, narrow boards.....and hew a finish it on top of that?