Hi
At the Bury club we use two 20' containers placed end to end. The top sections have been decked out with handrails and mesh for the rostrum. One container contains race-control with the other being used for storage.
Here is a picture of the final thing. We did consider having a cover to it like the rostrum on our old track, but being in a public park, this attracted undesirables in the evening taking shelter and throwing their cans/bottles onto the track.
http://www.flickr.com/photos/6380526...57626773129999
Hope this provides some further inspiration. I do not know the costs as we already had the containers.
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Associated B44.2, Nosram Pearl Evolution ESC, Fusion Exceed 6.5T , 4200 Lipos, Savox