about rates

Hi, everyone:

if leased area is <=100 square meter---------No subsidy
If leased area is >100 square meter----------Subsidy is $1/ square meter
If leased area is >200 square meter----------Subsidy is $2/ square meter

Now, If the area is 150 square meter, the subsidy should be $50

But the above formula can also have another unintended meaning: that is, the subsidy is $150 when the leased area is 150 square meter.
My question is: How can I avoid this ambiguity, by adding some words to the above rates?

Best wishes

Leased space up to 100 square meters---------No subsidy
Every leased square meter over 100 square meters----------Subsidy is $1 each
Every leased square meter over 200 square meters----------Subsidy is $2 each

Thanks a lot~!