There are several options available for licensing Microsoft systems on a HomeLab.
Many Microsoft products are available with 180 day evaluation licenses. Additionally Technical Preview versions are often available for upcoming platforms.
Microsoft offer several SKUs of the Microsoft Developer Network subscriptions, however several of them (including the most suitable- MSDN Platforms) are only available through Volume Licensing, which may not be suitable for a Homelab environment.
Exact details are subject to change so check the MSDN website for the latest details and what is best for you, but as an example in April 2016 Microsoft offered "Visual Studio Professional with MSDN" which includes perpetual Windows (Client + Server) and SQL Server licensing for $1,199/£825 list.
Azure Dev Tools for Students
If you are a student or faculty at a qualifying institution (basically a School, College, or University) you should be able to get Microsoft licenses for your lab through the Azure Dev Tools for Students scheme. These include Windows Server, SQL Server, and Visual Studio.
This scheme was formerly known as Imagine, DreamSpark and before that MSDN Academic Alliance.
See https://azureforeducation.microsoft.com/devtools for more information.
The standalone Hyper-V hypervisor (without a Windows Server OS) is available free.
Obviously you could also visit your local computer shop and purchase full retail licenses, but this is probably the most costly option here.