There are two ways to write conditional if/then calculations in Cognito Forms.
if <condition> then <true result> else <false result>
<condition> ? <true result> : <false result>
For your specific example, lets assume you create a calculation outside your repeating section called
Total Weight with the calculation
=Packages.Sum(Weight) that sums up the weight of the items in the
Packages repeating section.
You can then write the following calculation to based on your example:
=if Location = "Austria" and Destination = "Ireland" then
if Weight <= 10 then $27 else if Weight < 20 then $29 else ...
If you have a ton of options like this, I suspect this would be very difficult to work through. It sounds like you want to be able to look up a value from a very long table of potential values. Please provide feedback to this answer and I will be glad to refine my response.