I can't really speak for Lexus, but my V40 cost £30k new with extras, I paid £18k when it was 5 months old/5,000 miles, I kept it for 5 years & Lexus gave me £7.5k with32,000miles on it in immaculate condition. That would be quite a loss if you bought it new.
I hope my IS300h holds its value a little bit better, although I bought it pre-reg with 6 miles on the clock with quite a discount from new so happy with that, I have decided if the price drops too much I will just keep hold of it as I am hoping it will live up to its reputation as being one of the most reliable cars on the road.😃
Good luck with whatever you decide, but I would urge you to try another dealer & believe me there will be movement on the price even with cash, I know because I managed it.