You might assume that because the technology involved in manufacturing optical fibre cable is more complex than copper, installation of fibre networks would inevitably be more expensive than using copper. However, with the advent of CAT6 cabling means that copper is getting faster — but at a cost.
There are environments where copper is at a severe disadvantage; take an industrial environment with a lot of electromagnetic interference; copper cable in this type of environment will need a lot of protection, incurring extra cost, fibre would be totally immune to such interference.
Environments requiring long cable runs of 180m or more can mean that the cost of repeaters and outdoor environment cabling will outstrip fibre costs. If you want to test this for yourself, an excellent resource is the TIA Fiber Optic LAN Section which provides a cost model (you need to give email details) to help you separate out the copper vs fibre dilemma.