prices can change daily and sometimes even hourly...a few weeks ago we actually purchased our return tickets before our outbound tix because the price dropped dramatically for a brief period on the specific flights we were eyeing...we eventually bought the outbound a couple weeks later when those fares also dropped briefly...we prefer to fly through Miami from Houston

oddly enough, it's usually cheaper to fly out of Austin vs. Houston, even though it's almost 200 miles further west