Before you even consider going to Spain, take a look at some of the beauty it has to offer first.
Literally my closest cousin and I were at home, on the couch and thought, what should we do this week? She said let's just go to Spain, so we made a leave within two days.
This was one of the most spontaneous things I'd ever done; she'd always travel but for me, it was the most amazing thing.
We stayed in the amazing place of Las Ramblas in Barcelona. This place is honestly one of the most funnest places to be; especially for young adults.
You can budget widely and stay at a budget hotel or grab a hostel, to crash in. You can find some really reasonable ones in the city, they are not all that bad.
The hostels are kept very clean and well maintained. We stayed in Plaza de Catalunya was very comfortable, clean and welcoming. You have your own bathroom, bedroom, lounge area and easy access to outside; so that was a bonus for us.