It means that they all would have different opinions about Economics and could not agree.

That is funny! 1) reach can mean "to extend to" If all the pencils in this pencil cup were laid from end to end, they would reach 5 meters. [pencils put on the ground one after the other, total length would be 5 meters] If all the hot dogs in this pack were laid from end to end, they would reach from one wall of this room to the other. 2) In the expression "reach a conclusion", reach is used figuratively, as if a conclusion is something that is at a distance, and must be reached. "Reach a conclusion" means that everyone would generally agree on something. After an hour of discussion, the jury reached the conclusion that the man was innocent. Economists are notorious (famous in a bad way) for being unable to agree with each other on anything. So this sentence is cleverly mixing two uses of the word "reach", to say that economists often disagree about everything.