There are two ways to use a Price attribute in ACBC: 1) Summed Pricing, or 2) Standard Price Attribute. I'm going to assume you are using Summed Pricing because you are talking about price increments per level.
First, let's make sure you are talking about the Summed Pricing approach. In the Summed Pricing Approach, you add an item to your Attribute List for Price. Then, on the Attributes tab in the ACBC settings, you click in the "List of Levels" column that the Price attribute is "Summed Pricing Attribute". Next, on the Pricing tab you specify a Base Price, a percent random shock (usually +30% to -30%) and other settings that govern price (any decimals of precision to show, any rounding, etc.). Per each non-price attribute, you can specify that each attribute level adds or subtracts a certain price amount from the base price.
Now then, you don't need to add or subtract any price amount from the base price for an entire attribute or any level of an attribute. For the attribute level in which no adjustment to the base price is to happen, when you use the drop-down control on the Pricing tab to select that attribute, just leave the level blank or type a zero for the row in the "Component Prices" column.
This is not actually a "prohibition", because we are not telling the designer to prohibit one level of one attribute from appearing with one level of a different attribute. Specifying that a certain level should not have any additional incremental price added to it in the Summed pricing does not change the degree of orthogonality of the experimental design.
Please let me know if you are doing something different from my assumption of the use of Summed Pricing above.