This is the 913th most frequent Italian word.
costa
"Coast" or "rib" (depending on context).
In this context, 'costa' is used to mean 'coast' or 'shoreline' as a geographical term.
La costa italiana è famosa per la sua bellezza.
The Italian coast is famous for its beauty.
'Costa' here is derived from the verb 'costare,' meaning 'to cost,' and it refers to the price of the book.
Quanto costa questo libro?
How much does this book cost?
Here 'costa' metaphorically describes the effort or burden rather than a monetary cost.