According to http://www.nasa.gov/pdf/622643main_FY%2013%20Budget%20Presentation.pdf NASA's budget accounts for .48% of the budget.
We propose doubling the budget for NASA from the current $18.4 billion. This will facilitate not only Mars exploration, but Lunar exploration, space vehicle innovation, asteroid defense, anything that NASA sees fit.
During the 60's, when the space race was on, kids dreamed of going to space, and out of those dreams spawned the technological revolutions and enmities we enjoy today. Today, America is lacking in the programs to inspire kids to pick up engineering or sciences.
Understanding the space program's effect on American culture makes it difficult to understand why it doesn't receive more federal support.