Welcome Angela.
As to the lighting girders, you can build those out of either wood strip or styrene product. Think either basswood or Evergreen/Plastruct. Both would be available at a big hobby or model railroad store, or can be ordered online.
For the barn in that size, probably going to have to build it. Balsa and basswood are your friends there. If you have a model rail club nearby, contact them, most have someone who is good at building and girder construction techniques as they do buildings and bridges for their layouts.
Others will chime in on figure availability, that is way out of my wheelhouse.
As to a trike, might take a look at the Can-Am Ryker.....my lady has a 600 and loves it, she thought the 900 would be a bit much for her. She got hers new for around $8500 US, and some used are somewhat less.