I bought my IS sport 2001 about 5 weeks ago, it had 63000 miles on clock and i got it fot £5750, which was a bargain. The car is in mint condition and has 2 years warranty. I knocked the price down a bit but the guy had to sell really quick due to financial problems so guess i was lucky. :D
You'll be looking at between 6-7 grand for a IS sport with 60-80000 miles.
I wouldnt worry too much about having high mileage with Lexus they last upto 300,000. As long as the car's been serviced reguarly.
As for boy racers i wouldnt worry too much as Leuxs isn't really a boy racer car and you tend to find little chavs can only afford nova's and fiestas
Just make sure you spend time looking over the whole car, check for noises and play in the wheels. Look at old MOT's to see if the car has failed on anything.
Also check service history as to what has been changed in the past.
You cant go much wrong with a lexus so sure you'll be very happy with on purchase.
You do have to go past 4500 rpm to get the best out of the engine but cruise very well at lower revs. 6th gear is brilliant on motorways and general driving. :D
Hope this helps, if there's anything else you need i'm sure you'll find the help you need on here, happy hunting. B)