Larry, congratulations on the fair gig!
I'd pay $8 to $9 with no questions asked for your 9" margherita. The pies look very nice (dittos for the family)...quite authentic looking. I think $8 is likely the right number.
While $6 to $7 would be a good value, it would not be a good value for you, especially at $6. A lot of work will be required.
Finally, I agree with keeping the selection of pizzas simple and limited, for a variety of reasons. I agree with pepperoni as the topping, being America's favorite topping and all. Two pies keeps your prep work down and expedites the workflow at what will likely be a very busy fair.
For a simple way to offer more pizza variants, you may want to consider bringing some oregano, garlic-infused olive oil (easy to make yourself) and some blocks of pecorino romano. These three items, combined with what you already have to make the margherita, would allow you to offer both a marinara and a white pizza (fior-di-latte, garlic olive oil, pecorino, basil). So for a minimal addition of ingredients and time, you could essentially have 5 pies on the board (marinara, margherita, white, white with pepperoni and the margherita with pepperoni). Somewhat surprising to me, white pizza is one of the more popular pies at my market stand (I do fior-di-latte, garlic olive oil, sea salt, basil and pecorino with a fresh grating of parmigiano-reggiano or aged Spanish mahon post bake).
Keep it simple and keep it high quality. Keep your product and image consistent with what you are already doing. And realize you are never going to be able to please everyone, so why even try. I think your pizzas look excellent....and likely taste the same.
Hit it outta the park!