Cost for purchasing full assets/ownership of app? HELP

[JoocyGoose Games]

Hello i am dealing with a freelance development company and i have been given a quote of '5 times the cost of development' for the purchase of the assets/ownership once the game is complete.

So if the game development was to cost me $20,000, it would cost a further 5x that amount ($100,000) to purchase the full ownership/assets.

The game i want developed does have a lot of valuable features and i see how they could benefit from using some of the code. But is 5x the development cost a normal average price for the ownership or does it seem like they are trying to rip me off?

any help would be appreciated
thank you