As all cables must be certified, and the Thunderbolt spec limits copper cables to 3M, your choices are limited.
Bit the bullet and spend the money for optical, or move your system closer together 😀
The copper cables do have logic on each end so it is not simply a plain copper cable with an mDP plug on each end. The optical cable is even a bit more complicated, hence the cost.
Just pretend that the optical cable is a high performance "Monster" cable. 😀