Microsoft's's planned acquisition of Xamarin could cost them as much as $400 million. The company revealed its plans to buy the San Francisco-based mobile app development tools creator earlier this week.

The numbers come from Bloomberg, which added:

"Talks between the two companies started late last year, almost two years after earlier discussions failed to result in a deal, the people said. The two companies have had a partnership for several years."

If the numbers are accurate, buying Xamarin would still be cheaper for Microsoft compared to earlier acquisition deals, such as its purchase of Skype for $8.5 billion and more recently the purchase of Mojang, and its Minecraft game franchise, for $2.5 billion.

Source: Bloomberg