This will get it done for you:
switch(r, 1, 1000, 2, 700, 3, 500, 4, 400, 5, 350, 6, 300, 7, 250, 8, 200, 9, 150, 10, 100, 11, 50, 12, 50, 13, 50, 14, 50, 15, 50, 16, 25, 17, 25, 18, 25, 19, 25, 20, 25, 10)
It's a simple place to points, and I'm sure you can see from it how to change the points for each position, the 10 at the end represents all the other ranks not defined.
Regards
Stu