How to make this simple comparative sentence right?

Question

There are 4 ways to express as below. I like the first one, but is it grammatically sound?

The average salary of the male group is $20,000, significantly lower than $30,000 of the female group.

The average salary of the male group is $20,000, significantly lower than $30,000 for the female group.

The average salary of the male group is $20,000, significantly lower than the female group of $30,000.

The average salary of the male group is ($20,000) significantly lower than the female group ($30,000).

Answer 1

Favourite answer

The average salary of the male group is $20,000, significantly lower than THE $30,000 average salary of the female group.

Answer 2

The average salary of the male group, $20,000, is significantly lower than the $30,000 average salary of the female group.

You might add how often they are earning that money i.e. $20,000/year or $20,000/month?

Answer 3

No, none of it is correct and I have to wonder if it's even true, but in the interest of editorial accuracy, I'll play along. 

The average salary of the male group is $20,000, significantly less than the $30,000 average salary of the female group.