Hey,
Well do your research if thats not the cheapest one around, then compare the prices with similar vehicles available with same spec and milage and age.
Stick with Approved Used, at-least you know its good enough for Lexus to sell, its good enough for you to buy. (Some may disagree, but you'll have better assurance buying from a dealer than privately.
If you cant seattle on a lower price, get something that will save you money in the future like servicing i.e. say include the next 30k servicing in the price
Or stuff you may want to buy after purchase i.e. the lexus rubber mats to preserve the original ones etc
Full tank of petrol/diesel, flowers for the ladie etc etc