I've been selling off my old books since Sept, but for the challenge I plan to use the rest of the money I make to buy used books at yard sales and library sales to resell. I only have a few left. The books that sell for the most are text books and reference types, so I'll keep my eye out for those when I buy. I sold one text book for $37 and had brought it at a library sale for $1.00. Most of the books sold between $3-$6. The most I'll pay for a book is $1.00 unless it's something I really want to read. The best part is I get to read all I want.