I bought a rubber one (not silicone, but rubber) off ebay for about $5.. it still keeps the original shape, and is black.. And doesn't add much to the thickness. I think eBay is your best bet for cheap but good cases.
I've been looking for a case too. Having a real hard time finding a good one to buy in person. This phone doesn't seem that old that I can only find a case online.
No longer available on Amazon, but I'm sure it's available somewhere. It's so easy to remove, yet it provides protection.. Great case if you frequently swap batteries like I do.