How to perform calculations similar to this page?

i need my customers to be able or order daily meal plans but also change the price. would be alot easier to explain to the phone do you have contact numbers?

this is what i need it to look like  http://www.progainsmeals.com/product/weekly-order-3-meals-a-day-for-5-days/ 

Unfortunately, we do not have a phone support. But we'll do our best to assist you here in the forum.

Now the link you shared seem to have a custom pricing for different choices in the drop down field. This is possible by using different available features that we have. 

Below are links to help you get started:

These are links on how you can perform calculations:

https://www.jotform.com/help/268-Conditional-Logic-Inserts-Text-Calculation-Into-A-Field 

https://www.jotform.com/help/259-How-to-Perform-Form-Calculation-Using-a-Widget 

Now if you wish to assign values on fields like drop down fields, radio buttons, check boxes and 

https://www.jotform.com/help/301-How-to-Assign-Calculation-Value

After you have setup the calculation, you can pass the final calculated price to your payment total field by following this guide: https://www.jotform.com/help/275-How-to-Pass-a-Calculation-to-a-Payment-Field. 

If you need more assistance on this, let us know how your calculation works and we'll try to assist you on this.

We'll wait for your response.