A modular system of bridge/viaduct columns. Any height and width between columns, just tell me what dimensions you want. Multiple heights lock together for alignement. Price is $10 per 2 columns and 1 cross brace. The white shown is 2 modules on top of each other so $20, Varies really depending on size.

A Marklin bridge shown for size. Looking at a deck system to go with them as well.

SEE BELOW 

Custom Bridge supports.

A modular system of Plate Girder Bridge bridge panels, can sit on the above columns or your own embankments etc.

Made upto 300mm in 1 piece or can be smaller, or joined together to make longer, single width shown but can be double track width if required. Price of $15 per 100mm single width or multiple of, made of 3 parts for you to assemble.

Black bridge shown is 400mm long so would span 380 mm as a guess, that would be $60. 

Open beams below but a panel available to seal over, that can be timber stained to resemble wood decking by you, $3 per 100mm or multiple. Peco code 100 track shown as example.