To Thrutch. Looking at your running cost, for the size of engine you have they seem about right.
Have you considered the following: raise steam to full working pressure using only wood. When full pressure is reached and a thick fire bed established, then and only then start to add the expensive coal. Do not be tempted to mix the two as this will result in a messy fire.
I know this is not feasible for loco's or road engines as the action of the blast pipe jerks the fire around, but it should be OK on a stationary boiler. Another alternative, if there is a plentiful supply is to fire entirely on wood it'll keep you busy but far cheaper.
I have always considered raising steam by coal (especially these days) as a complete waste of money
Try it a couple of times, I would be pleased 🙂 or disappointed 😞 to hear the results.