The prototype process serves many functions, but seldom is it perceived as a way to minimize cost and save time in the production process. But approached the right way the prototype process can be instrumental in clearing your way to production, and it can minimize the cost of the production dies.
As a rule of thumb prototype tooling is approximately 10x to 20x cheaper than a production die. So unless you are absolutely convinced that your part requires no design changes, it is cost-efficient to prototype, test and prototype again, making tooling modifications as needed to perfect and finalize your part design.
Caution: Do not rush through the prototyping phase. Allow yourself enough time to properly test the part, to tweak the design and to retest it before moving forward with building the production die.
It is far more economical to make the necessary design modifications in the prototype tooling than in the production die. There are several factors to consider when making last-minute changes to the production die. Modifications of any kind to the production die are costly. Production must be stopped to pull the die. This means costly down-time while the die is modified. Furthermore, the production life of the die decays with each rework; thus, your cost per part will begin to rise sharply.
Knowing the immediate and longer-term costs associated with making changes to the production die can provide the designer with the information needed to properly test and refine his final design before committing huge sums for the creation of production dies.