Easyjet from Manchester is usually about £120 return. I have stayed at both Ibis Styles (booked through Accor site) in Berlin. Ibis Styles are awful in the UK but unsurprisingly they are great in Berlin. Clean, comfortable and with a decent breakfast. Just had a look and they ranger from £50-£100/night so if you can get to Manchester then you should be all sorted £300-400.
I drove the first time to Berlin and it makes for a bloody long day in the car