What are the factors affecting the total cost of a bridge?

Lenght
Wideness
Height
Over water or just land?
Depth of the water
Materials used (metallic vs concrete structures)
Arhitecture (simple vs complex)
Maximum load
Type of traffic ( pedestrian only, cars, trains etc)
Price of the materials
Price of labour
Is it close to a populated area or not? (if not, you would need to re-locate work force with additional costs)
Supported by local authorities? ( cheaper authorisations costs, possibly some subsidies)
Availability of funding (lack of funding can increase the time to build with some fixed costs of the project still flowing in)
Temperature at the place of work (e.g. if build in a -20 temperature zone - north pole - it would cost more than in other warmer areas as you would need some special concrete)
Legal safety regulations
Local community support or disapproval ( they can organize protests which could lead to delays)
Existance of qualified work force in the area (if not there, relocating people from other areas would lead to additional costs)
Etc.