Where do you find value of Tom Sawyer book?

Ebay Tom sawyer is a 300 page 1870 book. The first ever written with a typewriter. The highest price I have seen was in an auction and the book was one of the first editions plus it was signed by the author. It sold for 350,000. Regular modern tom sawyer books go fot about $5.99 at borders. In the related links box below I posted the borders page with the book.