I was just thinking, there's an article posted somewhere on this forum about cold plasma being researched (it linked to Space.com so go look for it there).
A magnetic field by itself could probably repel solar and interstellar radiation but it would require tons of power, as you said. The other option, applying the idea of cold plasma would be to trap the plasma within a layer of the hull and they have shown it could be tuned to absorb or reflect radiation.