on our old fashioned Ls400s the UCAs ( upper control arms ) are about £550 each from Lexus but 50% of that for original Toyota parts imported from, say, Amayama / Rockauto .... and fitting isn't too much of an issue AND they last about 150k - 200k miles
NOW, your car is highly technical and no doubt requires some specialist attention for most mechanical and all other stuff .......... but at £1400 a corner, blimey, that sounds ludicrous
Are they MOT Advisory worn too at this stage ? could it be over zealous advisory by the Lexus main dealer ?
Someone hopefully, with a Ls460 will be reading your Post and bring some sensible " comfort "
Malc