€1200 a month you'd need to work in more than one place. You could earn that in a big city but rent is crazy, especially Barcelona.
Teaching in businesses you need a car, hours are usually before work/lunchtime/after work (eg some days my hours were 7.30-9, 9-10.30, 12.30-2, 5-6.30, in the same company, so lots of drive to and fro). Or in a big city you'd be on the bus/metro zig zagging about. I did it a million years ago when i was young and carefree, but now older with dc I don't have the energy.
Teaching in an academy is a different kettle of fish. You go in, teach straight through, go home. These are often afternoon/evening hours catering to kids, teens, uni students and adults.
If you can get a job in an academy then extra business hours in the morning then you can easily earn €1200. But for teaching 25 hours a week (i wouldn't recommend more) you also have to factor in: planning, photocopying (sooooooo much bloody photocopying), marking, travelling...
I'm still in Spain in the TEFL world so if you like feel free to PM me.
You can do the TEFL training course in just 1 month, either here or in UK.