If all you're doing is design, then you can download SharePoint Foundation for free from the Microsoft Website, as well as Visual Studio 2010 Express and SharePoint Designer 2010. These are the tools you will need.
Then look around for tutorials describing how to build a SharePoint development platform (there are plenty).
You will need a fairly powerful machine that can afford to give a Virtual Machine around 4GB of RAM, and Windows Server 2008 R2. This might be your only expense (as well as a VMWare Workstation licence).
For picking up Design stuff, you can get away with doing a "Basic" install onto your VM. Personally, I reckon this is ok but you'll see a lot of tutorials strongly advise against that as the installer sets lots of service accounts to unsure ones and the environment is unscalable. But in my opinion, like I say if it's for design stuff, you'll be fine with this environment.