It's just a clutch disc

http://www.helix-autosport.com/produ...poke-products/

Price will depend on the type of disc you want etc.

But you'd need to find out exactly what size you need, thickness, material etc to suit your input spline.

Some BMW's run a 10 spline, and lots seem to be 240mm diameter, same as a Cossie. But whether that spline diameter is the same as yours I dont know. Googling would suggest BMW might be a little larger.
The US Ford clutches that would use that spline all seem to be larger diameter maybe around 265mm ( 10.5" )

So really a clutch disc could be as cheap as any generic OEM replacement disc or a lot more for something fancier. Just depends what you need.