How much to chop a top?
A chopped 1936 Ford three window coupe is my favorite car of all time. As MARTINSR says it is not an easy top to chop. Look for a shop that has done one before or has done several similar cars. Look at their work and ask questions of the owners of the cars they have done. When you find a shop you feel can handle the work then you will be paying the "right " price for the job. If you can't afford to do it correctly now then drive it with a stock height top until you can. It will be worth the wait and you will not destroy your body. As well you could have the top chopped now and only do the bare minimum to get you driving and do the rest as you can afford too.
How are you planning to build your ride? Streetrod, tuff hot rod or tail dragging custom? Even though this is not my personal preference there is a beautiful three window tail dragger in the May 2006 issue of Street Rod Builder magazine.