I really need help with shipping.

I sell products.  My clients are 98% located in my area where they can pick up their products.  Occasionally I have an order that needs to shipped.  Is there a way I can set shipping costs if they complete a certain field like address?  I've been trying for two days reading the forums and google with no luck.  Please can someone help me.

This is possible, please check this guide: https://www.jotform.com/help/304-How-to-Add-Shipping-Cost-to-Payment-Forms 

Let us know if you need more help.