Set the price of the book as A yuan, Xiao Qiang's money as B yuan, and Xiao Yong's money as C yuan;

0.8+b = a； 2+c=a，b+ c < a； Because a, b and c are not negative numbers, when c is 0, a is the minimum 2 yuan; b+ c < 2.8； Scores don't count, so a < 2.7.

So this book has the most 2.7 yuan and the least 2 yuan.