Hubby came up with a brilliant partial solution... get a few rolls of heavy-duty aluminium foil, and a roll or two of sticky tape, and get to work. About half our windows now have a layer of foil, shiny side out, stuck to them (on the inside surface). He covered roughly half of each 'set' of windows, so we still get daylight.

Cost : About $6
Effort : OK, it's a bit of a pain putting it up, it took a few hours
Downside : We don't have such good views, the house is darker inside, and I haven't had to remove the sticky tape from the windows yet...
BUT
Effectiveness : Noticeably cooler inside for most of the day! PLUS the aliens can't read our minds any more.... ;)
