@Christian N, take a look at this video, which shows someone building a stand for an anvil with stock very similar to what you describe in your original post. If I were in your position, I would very seriously consider giving this a shot: it's easy to build, can be made with minimal investment in material (especially if you can scrounge scraps of 2x4 from a construction site -- with permission, of course!), and is stable and effective as a stand. I would recommend putting a couple of different radii on the different edges, rather than leaving them as sharp as in the video, but this is otherwise a very good design.