Build it cheap. Build it strong. Pick one.
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Build a bridge across the canyon, then send someone over. Your score is the money you did not spend, so the cheapest bridge that stands wins.
Tap a dot, then another, to lay a beam between them — or drag from one to the other. Tap the same two dots again to take that beam away and get the money back.
Road is the only thing anyone can cross on, and a piece of it only reaches the next dot along — lay a longer road and it is cut into pieces at the dots. Road with nothing holding it up sags and snaps. Struts are cheaper and just hold things up. The dark iron plates are bolted to rock or to a tower and never move; everything else is held up by what you built.
Press Go and the bridge sags under its own weight for a moment, then off they go. A long beam being squashed bends and snaps early, so short beams in triangles are much stronger than one long one.
A run fails if a beam breaks and the road drops away, or if the road sags so much there is no climbing out of the dip.
Get across and the next level opens. Your score is the money left over on all four levels added together, so go back and build each one cheaper. Who crosses makes no difference to that — they all weigh the same.