For the most part 2 band is more expensive. Rooney and Shavemac both feature 2 band hair in their top of the line brushes. Simpson only sells 2 band sparaticly as the hair is hard to source, and Rooney no longer makes them for the same reason. Simpson 2 band is a little cheaper than their Super 3 band hair, but as it is in limited supply its a crap shoot to find the exact brush you are looking for, or the price a given vendor might charge. Some expect a premium for having the last of a particular brush, while another vendor might have them on close out for their cost (Vintage Blades).
There are several structural difference between 2 and 3 band hair. The first and in my opinion the most important is diameter. 3 band hair is topically uniform in diameter from base to tip. Where 2 band hair has a very wide base (the dark part of the hair), and a slender tip (the white). This provides for much more backbone per hair than your standard 3 band. The small floppy tips are still soft to the face, but not quite as soft as most 3 bands of similar quality. If you face lather this is a very adventitious combination. Where you get a nice massaging feeling, soft tips, but skip out on the prickliness that a brush of that backbone might have. Thus a 2 band brush can achieve the same backbone as a 3 band brush, but with less hair needed. Also with the large diameter hair, 2 band needs to be soaked almost like a boar brush to become soft. They are not exactly harsh when dry, but they do soften up substantially after a couple minuets in warm water. Three band for the most part feels the same after just a couple seconds submerged water.
In simple terms a 2 band could be said to be a better face lathering brush, where 3 band would be a better bowl brush. Though many other factors play into this. Knot size, loft, handle, hair quality, etc, etc, play at least as much of a factor as hair type though. Just to prove this point, I have a great all around 2 band, and some good 3 band face latherers.
I almost strictly face lather with soaps, so for me two band is my personal favorite, but if you use mainly cream or bowl lather 3 band would most likely be better. Why pay the premium price for a tool that is not suited to your chosen task??!!?
If you were curious about a specific brush or even a couple brushes post them and we might be of more specific help for you. Also if you could tell us a little bit more your shaving style/gear preferences we might be able to sort out what might be a better fit for you.
