Taken from the Lexus website...
Service Name
Mileage
Price
Intermediate
10k / 30k / 50k / 70k / 90k
£295
Full 20
20k
£445
Full 40
40k
£495
Full 60
60k
£745
Full 80
80k
£495
Full 100
100k
£595
In terms of always having to have it serviced at Lexus, I believe that as long as you can show that the car has been serviced with original or OEM parts then you should be golden.
I get my oil changed every 5k but a friend at his garage so get a local garage stamp every 5k but go to Lexus every 10k. Lexus have never queried it and were happy to renew my warranty after inspection.
HTH 🙂