That and a new water pump every time you do a timing belt. This should only be roughly every 60k miles so if you're an "average" driver it should be about every 5 years (assuming you own the car that long). I work at a Lexus dealership and own an IS 300, this is pretty much standard on all of the IS 300's we see coming into the shop. Sure its pretty spendy if you pay to have it done at the dealership but its not all that difficult of a procedure if you are even slightly mechanically inclined. I did my last one for about $240 in parts, this was with employee discount of course and I did the labor with the help of a friend being that it was my first on the model. You should also replace the Accessory belt and thermostat while your at it being that both of those are pretty cheap and just good preventive maintanance. Most of all, please please please replace the rod clip, it's extremely cheap and easy to fix :D
