Is it possible to create a hidden field with a number that the creator of the form can set?

I have a text element that is filled with data drawn from other elements as a summary of the form results. I have a column for hours, cost per hour and then a total cost. I have filled the hours column with results from other answers, and I know how to calculate the total cost using a form calculation widget, but rather than entering the cost per hour in multiple places, i would like to set the cost per hour as the outcome from an element that i can reference using {number} (or something along those lines) (in the event that I want to change the cost per hour for future form submissions).

Is it possible to have a number element (hidden) that I can enter a number into before publishing?

Yes, that's possible. Just add the hidden field in your form and use URL parameter to fill the hidden field.

http://www.jotform.com/help/71-Prepopulating-the-fields-to-your-JotForm-via-URL-parameters

Example: In your form, let's assume the Client Name is the hidden field. So the URL is https://www.jotform.com/80640600662853?clientName=123412

clientName is the field name (should replace this with your hidden field after)

123412 is the value which you can change to anything you want