If it's coming out of your own pocket, just fly back in Econ.

Its only a 3 hour flight.

However if you need the tier points then fly business.

Note though I don't think they have I class specials like they do with BA, so the price difference between business and econ can be quite a bit.

If you don't need the tier points and miles and you want to go as cheap as possible, suggest you look at Jetstar as another option.