You can get a perfect low mileage one owner 93-94 ls for 7k. Those are the years you want because of bigger wheels tires and brakes, lower cladding, and r134 ac( if you want a first gen). The only probs you might have are power steering, and alternator troubles ( they are related... the power steering fluid leaks onto the alternator and kills it). There are really no other problems that would be differrent from any other car. You know motor mounts, suspension components, bushings. Finding a well cared for example is easy.
And unless your a perfectionist, repair bills wont be too high if you have a trusty mechanic. If can work on your car... even better becuase you'll never be in a rush since its a secondary vehicle. The LS is pretty easy to work on, but is tedious.
good luck on the search!
PS even high mileage LS400's shouldn't be knocked off your list. If they were taken care of they can be just as reliable at 200k.
Lexus published an article about a guy who had upwards 500k on his LS. Original engine and Tranny.