As previous post. Caribe Tours to Imbert, then publico to Luperon. All very cheap and easy. Only downside might be the waiting time for next bus and/or publico.
Correct me if wrong, but I believe Metro do not stop at Imbert. If they do, that gives another option.
There used to be a publico direct to Luperon from La Javilla in Pto Pta. I have not noticed one for many years so I do not know if it still runs. And even if it does, it may not be very frequent. If cost is not an issue, or you have companions or much luggage, you could commission a dedicated publico from the same parada. It faces Javilla Tours across Avenida Caamano.