Is your prototype quantity requirement 10 pieces or is it 250 pieces? Is it 10, and then 250? Is it 10 and then maybe 250? It is helpful for you to try to determine this, and to share this information with your prototype supplier at the quoting stage.
I have often witnessed low quantity prototype projects grow to larger quantity prototype needs. As the need for additional larger volume requirements arise for additional testing, pilot builds, marketing tests, etc., these parts are often produced with tooling that was really more affective in low volumes. If at all possible, you may want to discuss these known or possible quantity requirements with your prototype supplier. If a larger run will be required, the lower volume tooling my be able to be designed in such a manner so as to minimize the cost and timing associated with a tooling upgrade.
Furthermore, you can avoid the possibility that the lower volume tool is designed in such a way that it is not able to be upgraded in a cost affective manner. This could force you to re-tool or to live with the cost penalty of running the larger volumes from a tool designed for low volumes.