When I first started looking for an RX, I actually bid on a 2007 RX400h with 155k miles on it. I lost and it went for £6, 400 - ex-company car, lot of service history, just very high mileage...
Depends how brave you are....I eventually bought mine with 100k miles (ex-company car, FSH) and 18 months later, I've added only 10k miles. Just went through the MOT with only an advisory that suspension bushes may need replacing next year. I paid £9k...