I use Titebond III also, I have no idea if Titebond II would be equally as affective or not. However, I think of III as added insurance and piece of mind. It's always my preference to want to over engineer the situation, maybe not necessary, but better than the alternative.
Considering the volume I need, and the reasons for my becoming a Beek, the cost difference really isn't an issue for me. I can appreciate that if someone was large scale and profit was their primary motive, the cost difference would be an issue certainly worth taking a very close look.