As a BFA graduate in ceramics, I immediately go to clay as a sculpting media and I will suggesst low cost tools for this material to sculpt. If it is wood or another sculpting material, most likely my suggesstions will not be helpful. What a great aunt you are to put so much thought into this!
For handbuilding or sculpting clay he will need: a good sponge (natural sea sponges are the best but tend to be expensive so a round manmade sponge works well also), a needle tool (a wooden handle with a 2.5/3 inch metal needle top), a clay knife (a wooden handle with a long flat dull metal blade), an old hard toothbrush (this is used for texture and also to meld 2 pieces of clay together because clay when wet will stick together but as it dries if there is no scoring and slurry - mushy clay- the 2 pieces will pop apart), a wooden or metal clay rib (a kidney shaped piece of metal or wood for scraping or smoothing over the clay) and maybe a tool box to hold all of these items as they will get muddy and dirty and dusty with dried clay.
These are the basic necessities; he could use a clay wire (2 wooden dowels with a wire wrapped between them to cut pieces of clay off of the big lump or to cut pots off of a throwing wheel) but for sculpture it is not really a necessity. Also any found objects that might make cool texture could be added (combs, shells, pinecones, metal washers, forks, old typewriter keys; essentially anything that might make a lasting mark in the soft clay).
Now, I don't know about Michaels to buy tools. I've never bought them from any place other than community art centers or art school. So give them a try but if you cannot find what you need, you can check any local community center that offers clay classes.
I hope this helps some.
Fondly,
ann m.