How can I make a book case made of pallets without doing too much?

Pallets are kind of hard to work with. It would be easier to get some boards and brackets that fit into metal pieces made for the brackets. Or you could just make an elongated box and hang it from some of those gray metal brackets such as used in a work space. Keep your eyes open at Goodwill and such places and you might find a very inexpensive one. Or at yard sales. We have book shelves in every room of our house and some of them were found for free.

What is "too much?" Here are a couple links for ideas and to get you started. Have fun!

https://www.1001pallets.com/diy-pallet-furniture/pallet-bookcases-bookshelves/

https://www.pinterest.com/explore/pallet-bookshelves/

https://www.youtube.com/watch?v=6_L0PG8A2YQ

go on ligh and look up pallets. There's a million ideas; also many books that on pallet furniture, etc.

Pinterest has lots of versions of this, so you can pick one that suits you:

https://www.pinterest.com/pin/269090146464282881/?lp=true