That's not really a good way of measuring. The federal budget isn't some objective unwavering standard by which to measure cost. And it's not really true anyway. NASA had that size budget, but that money was split between several projects, not just the rocket. A more appropriate measurement would be dollars adjusted for inflation. Wikipedia lists the "project cost" as $41.3 billion dollars adjusted for inflation. And that includes all the launches, not just development. The SLS is projected to cost ~$10 billion through 2018 according to Wikipedia. At that link there is a link to a NASA document which estimated the cost of the SLS through the first 4 launches at $41 billion. Depending on how you want to measure the costs, SLS is sort of in line with Saturn. It's definitely not 1/8 as expensive.