It looks like you have a lot of options available to you. However, if you are able to come up with a clone of the PJ Garlic sauce that is only as good as that sauce, it makes no sense if the cost of the clone is in excess of the $0.75 that PJ charges for one of its mini-cups of that sauce. It seems to me that if one were to use real ingredients, like real butter and garlic juice, the resulting product should taste more like butter and garlic than if artificial versions were to be used. However, while some of the artificial flavors are not necessarily cheap, using real ingredients might prove to be more expensive. This is not the time and place to do a cost-benefit analysis, but I think I would be inclined to start with the Shank's artificial butter flavor, if only to rule it out if it does not replicate the "butter" flavor of the PJ Garlic sauce. That flavoring might also include a coloring agent that might make the clone product a bit more yellow.
I do not know if the PJ Garlic product contains diacethyl. I remember a case a while back where a person developed severe medical problems because of exposure to the diacethyl. I think it was in a work context, however, and that the diacethyl was inhaled while airborne. If PJ is using that ingredient in its Garlic sauce, I would think that it would be in solution rather than airborne.
When you have a chance, can you tell us what you paid for the Shank's artificial garlic flavor and the two different forms of Butter Buds, and the quantities of the containers?