hopefully it's ASP VB script
In asp vb script the example of code to use would be:
WA_eCart_ConditionalTotal(yourCartName, "TotalPrice", "category", "plants") < 10
where yourCartName is the name of your cart object.
you will use this code in the shipping tab of the eCart object.
for the trigger, select the Custom Condition evaluates to true options, and use this code for the custom condition.