Hi I am sorry but I can't get a valid idea of what you want to make from the one picture ! what is the other side like and is the volume between the sides filled. Based on what a can see and assuming by small numbers you mean in the low 10s 0f units have you considered glass fibre lamination or vacuum molding the molds for which are much cheaper than for injection molding.
you might even be able to make the molds using 3d printing.

In my experience having had many hundreds of parts made from Nylon 6 by SLS printing the parts cost rockets as the part size goes up. This because most bureau us the size of the bounding box of the part as the method of pricing the job,