What Steven said. I reckon the plugs would probably last 150,000km in the 2GR-FE... even in the 2GR-FZE, but sometimes it's better to be safe than sorry because you never know if they won't last that long. For the cost of them, I wouldn't exactly call the procedure expensive. If you change them at 100,000km intervals, you are looking at about $1 per 1000km for your spark plugs. Considering your oil filter works out to be around $1.33 per 1000km, that's not bad.