Sorry to hear about your problem Robert, I know people that suffer with this and it's very difficult at times.
I'm sure many will advise that the way to go for a very quiet comfortable ride will be the LS400, or the LS430, both available on your budget, and just as peaceful to drive as you can get, even compared with new cars. Obviously good tyres contribute to quietness. I'm not sure about the GS series,it's a bit smaller and I'm sure owners will give you their input too. And welcome to the LOC!