Consider what we've laid out so far. Considering the screens we've drawn and the fact that the owner was able to view and sign-off that this is what he wants, how many more questions are there to ask? Do we really need some Excel document listing out requirements or a 30-page Functional Design Spec (FDS) document to tell you exactly what everything is supposed to be and do? Wouldn't this be enough? Does it have to really be done in Photoshop and produced as a slide deck?
Consider also that what we have done so far has cost us a grand total of five Post-its, one Sharpie, one pencil, and 20 minutes. I believe the case here has been abundantly made that for most sites, this is all you need and you can do it yourself.
If the speed and simplicity of paper prototyping are not enough to convince you to step away from the keyboard, then consider two other options for rapid prototyping:
Balsamiq Mo ckups (http://www.balsamiq.com/)
A xure RP (http://www.axure.com/)
I personally recommend Balsamiq Mockups. The prototypes it produces have a uniform but hand-drawn look. This will accomplish the same thing as paper prototyping but with more consistent output and easier collaboration across distributed teams. Both of these tools can produce fully-interactive mockups, as well allow the user to actually click through the prototype. Ultimately, paper prototyping is still faster and anyone can contribute.