For a BX, I can tell you. For a different tractor, someone else more knowledgeable would have to respond.
Full set up? Top O the line blade, QH subframe assemble cost $2100 plus tax at Kubota. If you are fortunate, you can get the salesman to let you have it for around $1800.
Used? Rare as hen's teeth, but have seen them for $1300-$1700 in newer condition. Local demand and blade condition are the variables. It also depends on whether a big snow storm is forecast. They are generally sold with hours. Ask me how I know.