I dare say if it was genuinely for sale it would be priced a bit more competitively.
You have a point that not many modified cosworths etc.. sell for that kind of money, purely because few people who have that kind of money want what is essentially an old ford.
The reyland sierra being the car that it is may be easier to move on at big money as its a bit more desirable to some people than any other sierra of the same spec though, i guess.