Originally Posted by: ManteoMax 
Ralph Fulton addressed this question with Motorworldhype at E3. "The reason that we allow Legendary painters and tuners to set prices higher than the price limit because we want to reward those people for the work they do within the community and the content they create for others." but they'll look at the balance of the limits.
https://youtu.be/y5ekvoTwtP8?t=494 Thank you for this Reply.
Many of the good Tuners and Designers spend many, and I mean many, hours working on their designs and tunes. For some, this is the main thing they get out of the game. There are many Legend designers who do not even hold a high rank in the game, but have produced amazing designs with more then 100,000 downloads alone. Some, and I only mean some, of these tuners spend just as much time tuning cars for others to benefit from like myself. Having a notepad and pen out, keeping track of what works better or worse, making adjustments, and testing the car over and over as we make these adjustments.
This is big part of the game for a lot of people and Forza/T10 have noticed this and have chosen to reward those who put in the effort. Should the limit the amount, probably, but remember that ever car that these Legends and Elites are selling were available in a forzathon, or game expansion in which you could have acquired them. Also, if you want a certain car so bad and you missed the forzathon, do what they do and continually search for a deal and snag it quick. Just don't search once or twice a day and give up. Sooner the better as well, because the longer you wait, the harder it will be to get that deal.
The Auction is just another part of the game in which some enjoy more then others. It is a good lesson in Supply and Demand and real world economics. I usually start my cars at the minimum amount in which I won't suffer a loss, and usually set a max buyout according to what the cars are selling at.
Forza/T10 also control the Forzathon's, so they choose which cars are going to be in them and how often or how easy they will be to obtain.
"Integrity, is doing the right thing, even when no one is watching." -Anonymous and/or Paraphrase -Charles Marshall.