I just picked up a CM Storm Xornet from Amazon for $24. Initially the mouse was garbage because the liftoff distance was unbearably high, but that was fixed with a firmware update. So far it seems to be working flawlessly with the newer firmware, and I haven't had any of the issues people were having with the CM Storm Spawn and Mumble(maybe it has to do with the drivers for that mouse - the Xornet is driverless).
Also for reference, I picked up this mouse to substitute for my G400 while I wait for a new one from Logitech(apparently it's fairly common for the mouse to start disconnecting randomly). I may end up staying with the Xornet because I find it super comfy to use and I haven't seen any issues since I swapped the firmware.