Also to be completely accurate, this would have been in 2012 when the free version was Visual Studio Express and that was free for commercial use.
https://social.msdn.microsoft.com/Forums/en-US/f280e5b7-f17a...
In today's world -i.e. not for Windows Phone - I would probably not even bother with VS 2017 Professional for a two or three month project. I would just use JetBrains Rider (Macs/Windows/Linux) for $35 a month and use .Net Core and develop on the Mac.
If you really don't want to spend any money today, you could use Visual Studio Code on Macs, Windows, Linux.
You can use Visual Studio Community Edition for commercial programs, so long as:
* You're not doing so for an organization that has more than 250 PCs or 1 million USD in annual revenue
* No more then 5 users in the organization that you are using it for are using it for things other than open source, academic research, and classroom learning
> An unlimited number of users within an organization can use Visual Studio Community for the following scenarios: in a classroom learning environment, for academic research, or for contributing to open source projects. For all other usage scenarios: In non-enterprise organizations, up to five users can use Visual Studio Community. In enterprise organizations (meaning those with >250 PCs or >$1 Million US Dollars in annual revenue), no use is permitted beyond the open source, academic research, and classroom learning environment scenarios described above.
https://www.visualstudio.com/vs/community/