How to set up different prices?

Please check my form in this link https://www.jotform.com//?formID=session

How can I set up a diferent prices in the same Item, where size mark a diferent price.

Regards

You can setup different prices in the same item by enabling Special Pricing.

Here's a guide on how to add options and use the special pricing to modify their prices: How to Add Options to Payment Forms?

You can check out this demo to see it in action: https://form.jotform.com/62131136999966

Please let us know if you need further assistance.
Regards.