Spain is at its best when the sun is out but you aren't sweating through your shirt. Late spring or early fall are the sweet spots. The tapas are cheap, the streets stay lively late into the night, and the pace of life is slow.
A typical flight from the U.S. costs about $640. Instead of waiting until you have the full amount saved, we can look at it differently. You can book the flight now and use a 0% intro period to pay it off in small chunks while you plan your route through Madrid or Seville.
This isn't a free ride. If you don't pay off the full balance by the time the 18 months are up, the standard interest rate kicks in on whatever is left.