Amazons Kindle MatchBook service has gone live today, allowing customers to buy a heavily discounted Kindle copy of physical books theyve purchased from the online retailer. Prices range between free and $2.99, offering a quick and cheap way to expand your Amazon ebook library. And on that note, theres good news: Amazon says that 70,000 books are enrolled in MatchBook at launch, dwarfing the original 10,000 titles it announced last month. …