Pairwise adding tuples in a list
Review


No need for all these intermediate temp variables

You loop over a and b to append to the result which is unnecessary.

Only afterwards you create the products but this can be done before.
The sort is not needed if you keep a running minimum
Use a if __name__ == '__main__'
Consider adding Docstring and Testcases, (or both in the form of doctests) to make the solution more understandable/testable
Read PEP8 the python style guide


Functions and variables should be snake_case for instance



Revised Code

def optimal_shipping(a, b, target):
    """
    Finds the optimal shipping by compairing pairwise lists to the target sum

    &gt;&gt;&gt; optimal_shipping([[1,2000],[2,4000],[3,6000]], [[1,2000]], 6000)
    [[2, 1]]
    &gt;&gt;&gt; optimal_shipping([[1,8],[2,7],[3,14]], [[1,5],[2,10],[3,14]], 20)
    [[2, 3]]
    &gt;&gt;&gt; optimal_shipping([[1,3000],[2,5000],[3,7000],[4,10000]], [[1,2000],[2,3000],[3,4000],[4,5000]], 10000)
    [[2, 4], [3, 2]]
    """
    best = 0
    for i, x in a:
        for j, y in b:
            if abs(x + y - target) &lt; abs(target - best):
                best = x + y
                res = [[i, j]]
            elif x + y == best:
                res += [[i, j]]
    return res

if __name__ == '__main__':
    import doctest
    doctest.testmod()


Note
If those lists prices are in ascending order, maybe something with a bisect search could work.