If you have access to a laser you can make laser-cut own speakers out of 1/4" plywood.
If not, you can use online laser cutting service such as Outfab and cut it out for under a hundred bucks.
You can use old speakers for the components like I did, or purchase the speakers and amplifier from your local electronics store.
An old stereo system should have everything you need.
Step 1: Harvest parts
I got my speakers and amplifier from old speakers that sound pretty good but are hideous.
After taking the old speakers apart, analyze them and trace where the power and audio signals go. You'll need to know what to connect where.
Step 2: Design and Laser-cut
I uploaded the design in SVG format to http://www.fabout.com
You can customize the design before you cut it.
If you don't have a laser cutter you can submit it to online laser cutting service such as Outfab (3sqf costs $92 including shipping.)
Step 3: Parts
These are all parts necessary for the assembly.
For fastening the plywood I used 1/4" square nuts and 6/32 3/4" Torx screws.
I also sanded the wood to make it smooth but also so it fits in the slots.
By design, all slots were made smaller than the thickness of the plywood, so that everything can fit well after sanding.
Step 4: Assembly
Now the easy part - just put everything together like Lego, solder the power and audio cable and screw the sides.
I also put some hot glue on power and audio cable inside in order to prevent them from being ripped out.
Step 5: Done
There it is, a custom laser-cut speaker box.
You can stain it or finish it in order to match with your decor.
You might be wondering why I put those rectangles at the top - they serve two purposes: one is to keep people from blocking the vent holes at the top with flat objects, and the other one is to make the speakers stackable (I should have put some on the front and back too).
You can also put a honeycomb or other patters in front of the speakers if you wish to keep them hidden. You could also use some thin polyester fabric and stretch is between the plywood and the speakers.