Right now, Delta is offering cheap flights to Spain from all over the USA, including my home airports of OKC and Tulsa. I just booked on for $400 in March 2017 to Barcelona from OKC, which is very cheap.
There seems to be availability from many US cities, with the exception of Delta hubs, this means Delta is attacking other carriers. There also seem to be availability all over Spain as well. different dates bring up different prices so you have to play around to get the best deal. Remember, Spain is the home to the low-cost carrier Vueling and others as well, so if you want to go all over spain or elsewhere it will likely be very cheap, less than $100 likely.
Use google flights to play around with dates and times, but I found it, surprisingly to be slow at updating, so I went to Delta directly and did an advanced 5 week search.
Keep in mind that Delta, and many other airlines offer a 24 hour cancellation. THis means if you change your mind, you have 24 hours to get a full refund.
ACT FAST! Remember you can cancel in 24 Hours if you change your mind or find a better deal! This is also a good way to rack up miles and elite qualifying dollars and miles with Delta.
Thanks for reading!