try to negotiate it down. dont get the 4.4i as others say, preface lift 4.4i has worse engines than the 3.0. if you want v8 engine, buy the facelift 04+. $17,500 to $18,000 is the right range for the 2002 3.0i. before you buy, check these items: cv boots (torn boots), water pump (leaking), thermostat (temp needle pegged to the right after 5 mins), dead pixels on cluster or mid, battery, alternator(measure the voltage), listen to the transmission for bad sounds(make sure there is no sound from transmission, reverse and foward shift smooth), windows regulators(check them all by rolling up and down), heavy steering wheel (sounds like rubbing jeans together), brakes, knocking sounds in engine bay, open oil cap and the dipstick to check if there is a milky liquid there (signs of oil seperators failing), check coolant to see if oil mixed in there too, check for leaks on coolant resevoir, washer fluid tank too. lock and unlock all door using remote to check doors actuators, lock and unlock using central switch inside to check the central locking system. check for oil leaks too.
those are very common problems on the 3.0i that you should pay attention to before purchase. and good luck deciding, dont get the 4.4i this old.

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2002 X5 3.0 Siena Red
Premium, Cold Weather, Rear Climate Packages, 19" Wheels
Aluminum Running Boards, Clear Tail Lights, Clear Side Markers
Titanium Kidney Grills, Titanium Trunk Lid, Xenon Headlights
4.6is X5 exhausts, 35% Tint, Aluminum Pedals
2005 530I Mystic Blue
Premium Package, Sport Package, Xenon Headlights
18" Sport Wheels, 35% Tint all around
Mods to come: M-Tech Front Bumper, M5 Side Skirts, M5 Rear Bumper
Quad Exhausts, Style 172 19" Wheels