Thanks!
Well, the cost depends mostly on which materials you're going to use... I do my bellows out of leather: with little care they will last decades. Yeah, they are not as cheap as others made of plastic and nylon, and I must travel overseas each time I need to stock, but I know they will not let me down unexpectedly. I found it just a matter of taste and the quality-price relationship you want to obtain.
People pays for this kind of thing (amazing, but they do... This one went for almost 100GBP s/h included...)
For patterns, I found that a combination of strong cardboard (made out of a packaging box) for the full size, and simple cardboard (made out of a package of cookies) for each section does the trick for me. Balsa wood in different thicknesses is also useful, and my "molds" are made out of it.
I have done mostly Agfas, lots of them, and a few dozens of others (Iskra, Balda, Plaubel, Welta, Fuji...). Once you get the knack, they're not that hard to do.
Seems that you are also getting on track, nevertheless don't hesitate to ask if I can be of any help
🙂