If you have not already chosen your designer then now is the time to have a preliminary meeting or conference call with your shortlist. I suggest that you make your decision on designers based on your feeling from this first meeting. At this point no one has spent too much time or resources and you can easily turn away without engendering bad feelings. Storyboards are meant to be rough and will most likely be hand-drawn. You should make sure to decide beforehand and quite clearly what form they should take.
Many places charge for formally mounted boards.
You should also be aware that at this point you have passed the point of speculation and should be prepared to pay for the work you have had done even if you turn away. You have, after all, asked for a designer to design. If you are not satisfied with the designs as they are supplied say so right away and work it out, it is in everyone s interest to do so. A word about supervision. As frustrating as it may sound you will more than likely slow things down the more involved you become.