RUSH book question - Math II

<p>I'm looking to buy 15 Realistic Tests for the SAT Subject Test Math, Level 2 but I'm not sure what edition to get. Can someone point me in the right direction for the best guide? Do the guides really change all that much each year or does the book stay relatively the same? Also, would it be worth it to buy the newer editions for more $ just for the 3 fully solved bonus tests? I'm somewhat trying to pay the least for a quality book. Thanks everyone.</p>

<p>Does anyone happen to know?</p>