So, I've just burned the last bit of one €200 load of solar-dried firewood over a 134 day period, through a dismal winter - that's effectively just €1:50 per day and it keeps the Shed usable every day.
In fact, I still have some small bits left to start it tomorrow, but that's balanced out by a couple of lumps from the other new load - in case the cat comes back today.
I will give my source a ring in a while, when I know I'll be here and he can bring a new load when it suits him. That can be drying right through the summer, then.