you can go on their website to get 1 free full length test. after that, the cheapest way is to buy a new book. if you buy a used book, the previous owner will have to give you his/her login information in order to access the free tests. i don't believe you can re-register a book that has already been registered once before. otherwise, you'll just have to buy another new book - they are about $20 on amazon (this is how i bought mine).
Should i necessarily have to get the book from amazon/mgmat store?
Can I get it from some other known e-tailer in my country to save in shipping?