Hi Eric: chris Bolton here from the Big Enchilada.
Most of the large bulk lots sold on EBay are basically junk lots, that while they may fill many folders, and some may even be somewhat attractive, probably won't do a lot for you. I built up a collection of Mexican banknotes over almost 30 years, many at a very low cost. Many banknotes from the private banks of the 19th and early 20th centuries are still inexpensive, as are the notes of the Mexican Revolution, and they are attractive, with beautiful illustrations, many prepared by the American Bank Note Company of New York.
On the other hand, any established coin store can help you get started with much better starter packs of international bank notes.
I would recommend you start out by deciding what type of notes you want to collect: World banknotes, trains (ask Mark Todd, animals (look for African bank notes for exotic animals, and so on. The options are endless.
You are much better off buying a few notes at a time and let your grandson learn from them, and hopefully take a greater interest in them.
Anyway that's just my two cents worth. Let me know what you decide to do and I could help you with Mexican notes.
Best regards
chris bolton