I do some wood working as well as modelling, and I can tell you not to be turned off or intimidated by making your own bases. In addition to the suggestions already posted, you can by plywood or pine rounds or squares with finished edges in craft shops.
To roll your own you can get oak, pine, maple, cherry, you name it at your local lumber store.
You can use a router to make edge profiles, but if you don't have one it is a major cash layout (like all tools, buy cheap and get comparable results). Also, if you haven't used one before, there are some tips and techniques for getting good results that don't come with the instruction book.
You could also use a table or band saw to chamfer the edges. This gives a nice finish, also some where to mount a brass plaque if you are so inclined.
Use a water based stain and a matching clear coat over that to seal and finish the wood.
Most lumber stores have diy days where you can watch demos and ask questions of experts. Check that out if you can.
Once you decide how deep you want to plunge in please feel free to come back with more questions. If I can't help I'm sure others can.
Good luck,
Bruce