If it was mine, I wouldn't sell it unless someone pays me 1 billion dollars, in bitcoin, which is around 120k bitcoins.
But that's only me. Some other guy wouldn't sell it at all or sell it for $50k.
I think $1billion is a fair price.
Checking some other application that determines the price of that domain, it could not go $500 million
BITCOIN.COM TRAFFIC WORTH
We estimate the website value of bitcoin.com is currently at $ 211,715 USD and reaches roughly 48,524 unique users each day that generate 96,673 daily pageviews
the number one social media site is only worth more than $300 million
http://www.siteworthtraffic.com/report/facebook.comWe estimate the website value of facebook.com is currently at $ 393,338,737 USD and reaches roughly 23,331,426 unique users each day that generate 179,606,316 daily pageviews with a daily revenue (from advertisements, i.e Google AdSense) of $ 179,608 USD approximately. According to Alexa (the Web Information Company) the Global Traffic Rank is 5
so if the number one social media site Facebook cannot go over 500 million I doubt Bitcoin can too, but it's only ten years as adoption is progressing so the price will increase every year.