i spent 17500 a year ago, stock as, nothing touched not even the sound system
first thing i did was service everything, 100k service, plus every fluid, plugs, brakes, gave it a good detail and its one of the best, since then added wheels and a few other little mods and you can see the pic below
so yeah id say 17k, if you want a less popular colour like white maybe 15?
just dont buy off someone dodgy, someone straight up that will tell you everything about it.
and dont buy the first one you look at, look at heaps then you can tell whats good and what has had the clocks wound back, for example seats and steering wheels will be in worse condition then others and engine bays will look worse then others.