Hi,
there is essentially two price grades.
The most expensive is forged steel. Forging is humanities oldest and still the best way to get high strength steel parts, like chucks, tools and so on.
Downside is that its really expensive.
The lesser option, or at least cheaper option is to cast, ranging from grey iron, the cheapest, through SG irons, right up to cast steel, with the price increasing
as the strength increases.
In the case of Vertex most of their chucks and vices are made out of Meehanite, a really good grade of cast iron. Its not as strong as steel, especially forged steel,
but it costs way less. Were you to use a lesser grade cast iron you can make them cheaper....and it seems that is what the Chinese do. Pay you money and take your
pick.
I paid $157NZD for a 100mm 3 jaw, I would expect to pay $400NZD or more for a 100mm forged steel chuck, if they even make little baby chucks by forging?
Craig