This one is a bit smarter if you are after a 400, and not fussed about a saloon or tourer.
https://www.carandclassic.com/l/C1655859
Price reflects condition. Average price for an average condition S/C is about 13-16k though, looking at prices over the last couple of years. More for very low miles or a flip colour Monogram with 100% paint.
Bit out of the way for most, but there is this one in Australia,
https://www.carsales.com.au/cars/det...E-AD-16082159/
Equivalent to £17.5k. They are the only known 3 S/C cars for sale just at the moment.