I would recommend the Sketchup Free route. Or if you need to get info from SU to AC, you could install the SU Pro version to use the exporters (like DWG) while the trial period lasts.
Actually, I don't think that the ArchiCad SketchUp importer is quite ready for prime time. Even very simple model imports have a lot of extraneous geometry like unneeded Wallhole objects that take a lot of time to clean up. It is really best for creating nonparametric GDL objects like special windows and doors, but whole buildings are best done in Archicad from scratch.
If you want to model a building in SU for import into Archicad, the model should be created with that in mind: Preferably it should have only the exterior shell, with horizontal section planes for floors. Windows and doors should be modelled with no reveals.
Anssi