Hello Vanessa,
Do the shipping prices add/cumulate?
If you use the "price per product" the price will be cumulative, in your case the solution will be to create :
- 2 warehouses
One for your normal books with free shipping
One for big international books with a shipping price for [0 - 100] € and free shipping starting 100€
- 3 shipping methods
One free shipping method for normal books and with the first warehouse.
One shipping method with a fixed price, with the second warehouse, and with a "maximum price" of 100 €
One free shipping method with the second warehouse, and with a "minimum price" of 100€