It always shows the lowest available rate. So all you should need is a less than. However the zero weight thing could be an issue. It will assume a zero weight is digital goods and won't charge shipping. Is it possible to have a zero weight in your cart?
So for the bottom two you could do:
if weight < 24, $20
if weight < 10000, $30
The zero weight option I would have to look into for you. I think I have your ftp information still, so I can probably just get that set up for you. Are those the rates you want?