Couple things- the LF-A doesn’t have a bigger engine than the IS-F. The engine is smaller actually. 4.8 liters versus 5.0.
The engine is a “monster” yes, maybe in terms of technology but not in overall size or torque. As a small V10 capable of revving to 9000 rpm, yes it’s unique, but for less than half the price, you can get a really nice looking car with a V10 revving out to 8700 (R8 5.2).
What makes this car unique is that it was designed and built at a company that makes its bread and butter with soul-less vehicles that are more like appliances. (Don’t take this as a knock on Toyota/Lexus, I appreciate them just as much as you and the next guy)
But that’s one of the main reasons it costs so much to produce.