See if you can take the car to the dealer and have them run diagnostics on the car. They can also pull the service history on the car, assuming the previous owner had their service done at Lexus. Of course, they'll charge you a few hundred for this but if it gives you a little more peace of mind before making the purchase, it is worth it. I would still caution that this procedure won;t find EVERYTHING that is wrong.
Things to watch out for: condensation in the headlights and rattles in the dash/glovebox. These are minor things but can be an issue. Year wise, your car should still be under warranty but the mileage might not. Double check. If somehow, it is still under warranty, I'd get these annoyances fixed. The condensation is hard to tell unless you are in the right weather conditions. The rattle is obvious if it is there.
There may be a few other things that may be slipping my mind.
As for the 60k service, it should be between 800 - 1300 depending on the dealership and what they are listing as part of the service. There should be a list of things required in the manual. You can actually select things that you can do and go in and have the dealer perform the things you want them to. Just talk to the service advisor. You can probably whittle the price down to between 400 - 600. You just have to do the rest yourself. Since you are just buying the car, it may not be a bad idea to do some of the service at the dealership to have them look over the car.
I have a GS300 with about 74k miles on it. No major issues. I would not hesitate to recommend this car to anyone.
Good luck.