Tough question. I buy the materials and hardware in bulk, and each bait can use more or less of them. For example, I buy my epoxy in gallon jugs, which is enough to make a whole lot of baits. Wood, hooks, split rings, lead shot, eye screws and wire are the same way. I've never really averaged out material cost per bait, but it's quite minimal. Time spent building and painting them is another matter. Each one takes days to complete. Much of that is drying time for multiple coats of epoxy. Actual hands on time varies quite a bit from bait to bait. Cutting, carving and sanding a wood blank can take an hour or 5 hours. It all depends on size and how detailed you want to make them. I can shape and smooth a wood blank in little time. Carving gill plates or scales can get quite time consuming.
Here are some of the baits I've recently painted and/or made.