I have a question about all inclusive vacation bundles, rarer scenario, question about base price

This is very broad as there are many ways these bundles are priced. Generally though, the price per-person is quoted with a couple and so is discounted based on shared costs of the accommodations. Trying to book such a package for one will result in being asked for a single-supplement at the time of purchase.

All-inclusive packages are treated as designed for the common case of couples or families travelling together, so your scenario does not fit. They best thing to do is to call the particular resort and ask if they can charge you for an additional guest fee if you book a package. If not, then, you will have to calculate if booking two spaces even though one flight is unused would be more advantageous than booking the travel as a separate flight plus a stay for two. It does happen for many bundles that paying for more than you use will be cheaper and I know several people who booked all-inclusive vacations only using part of the lodging.