[spoon]

Here's an example from the PvK balance mod:

Characteristic Maintenance Aptitude Pct Cost := 150
Characteristic Maintenance Aptitude Threshold := 5
Characteristic Maintenance Aptitude Threshhold Pct Cost Pos := 300
Characteristic Maintenance Aptitude Threshhold Pct Cost Neg := 100

This means that you will pay the normal cost at 100 +/- 5 points. If you go over 105, you use the "Characteristic Maintenance Aptitude Threshhold Pct Cost Pos" value (which in this case is 300). If you go lower than 95, you use the "Characteristic Maintenance Aptitude Threshhold Pct Cost Neg" value (in this case, you get 100 points back for each point you lower it.

So the costs would be:
106%+ : 300
101-105%: 150
95-99% : -150
94% - : -100