The answer to your question depends on a number of factors.
a) How old is your copy of the book? If it is 50 or 60 years, it is probably not worth more than the paper it is printed on. If, however, your book goes back to the days when Robinson Crusoe was first published (1719), you may have a treasure on your hands.
b) What condition is the book in? The better the condition of the pages and the covers, the more it might be worth.
c) Is it a first edition? That means, is it from the first batch of the novel that was ever printed? First editions are always worth considerably more than any later reissues.
d) Is there anything unusual about your edition? Is it autographed by Daniel Defoe or some other famous person? Does it contain pictures that do not appear in most other editions? Does it contain any text that does not appear in most other additions?