I think what you are proposing can be done in PowerStore using the product options. Basically when it comes to the monogramming options you should have all three listed as values for the monogramming. You may want to offer another option of none as well. Then for the other options you would increase the price by 12. This way if any of the options other than 'none' for monogramming are chosen it will use the increased price you associated with the monogramming options.
I did some basic testing of this and I got a result that seems to be what you are trying to do so I think this is the best approach. It can sometimes be tricky to think of like this but basically different option combinations can have different prices for the same item so you just need to differentiate between the monogramming being none and any of the other values that would add the $12.