I cannot help you on the cost.

It sounds like a good length for adding a pusher axle.  That wheel base w/o the pusher may be able to (outer) bridge 4000 lbs more than a 6 ft shorter wheel base - if your extreme axle distance goes from 60 ft down to 54 ft.  If you added the pusher you may be able to pick up another 4500 lbs.  The pusher would add some weight and cutting the frame may take out some weight, unless you double frame it.

My '97 Freightliner is 240" and will maneuver tighter turns than the show trucks.  I wish I had some money to spent so I could try to talk you out of the number and into looking for something else for your needs.