l realize that a Lexus is a toyota, so it should be reliable, but how many miles could l get out of a 1999 Rx300? 150K? less?

With maintainance and caring for the car you should get a lot more. Than 150k...
It may need an engine rebuild but l have seen Lexus cars in the Uk go 300k and more.
They are not made like ford they are made to last as long as you dont thrash it..
Look after it it will look after you ..

Lexus is the most reliable car in north America for many years and if you take care of your car and if you drive in highway mostly you can even go to1 million K or more.
But if you abuse your car does not matter what car you have you can kill it quickly.
As my land lord drove his Lincoln for 963,000k and he sold it to a lady which probably did not check the oil and coolant and she blow out the engine in just 4 weeks.

After much research on this make and model (because l intend to purchase one) the general concensus seems to be that a Lexus can be expected to go 300K miles or more.

If you are looking to purchase, be sure to check Carfax on the vin number of the vehicle you are looking at.

l have no hesitancies about purchasing a 1999 Lexus RX300 with 100K miles in the 11,500 price range.

On average, it is recommended that a car should not go more than 20,000 KM per year. Anything more than that is too much milage. Lexuses are excellent cars, they do not break easily. Make sure that the car you want to buy has been through regular maintainence with the agent (Toyota guarage). You can find out at their office by giving them the registration number. l have a 2002 RX300. It is still running as the day l bought it. Go for it.

You can expected well over 300K miles or more.

Over 200k, Toyota is never die. Just change the Oil, service it once a year and your good to go. My 99' RX has 175k miles and never had a problem, My kid drives it every day.