Since you already know you will be only one of at least four food vendors (even if the prices the others charge are supposed to be higher than yours), I think you are unrealistic in thinking that you will be able to sell dogs to 50% of the total number of people attending.  If that estimated attendance and a wait of 45 minutes in line previously is realistic, I am pretty sure other food vendors will be begging to be included (maybe corn dogs, chicken fingers, pork chop sandwiches, smoked turkey legs, egg rolls or barbecue sandwiches, all meat items we have available at our Heart of Illinois Fair).  With this, you now could be competing with 9 other vendors.  And, as chefbubba asked, would you physically be able to sell a hot dog every 7 seconds all day long on Saturday?
 
I am not psychic, but a total of 2000 to 3000 hot dogs seems a far more reasonable number to me (and even that might be a high figure).  This would mean you are selling a dog about every 15 seconds on Saturday, and you are serving 1 out of every 6 potential attendees.