how can have prices in paypal sected by conditions.

Unfortunately, this is not possible in the Paypal Integration. A workaround for this would be to setup your product items using Radio Button (single selection) or Checkbox (multi selection) or Dropdown (single/multi selection).

You can assign a value for each option (http://www.jotform.com/help/301-How-to-Assign-Calculation-Value). 

Then you can calculate it in the form (http://www.jotform.com/help/259-How-to-perform-calculation-in-the-form).

After that, you can pass the total to Paypal (http://www.jotform.com/help/275-How-to-pass-a-calculation-to-a-payment-field).

Please try that and let us know if you need help with the workaround.