Is your controller case beat up and you wish you could get a new one? Do you want to mold your wideband into your dash or some other area? Want a white case? If yes, check out http://www.pactecenclosures.com/Plastic-Enclosures/HML.html
I busted open my case, since they glue them shut after assembly, and looked up the part numbers. I ordered one of each color and the total was just under $15 shipped for both.
I also noticed upon inspection of the boards that they are labeled “PLX Devices Inc. M200-M500 Unified Version 3.0”. This means it might be possible to upgrade your lower end controller to the capabilities of the M-400/500. I imagine this would work by buying the USB RX module. I haven’t found it for sale, but calling PLX might get you one. After that you have to solder the coax conversion cable to the board. This seems like it would be the hardest/most time consuming part. For people on a budget it might be worth looking into.
For users of the M-200/250 you might be able to add the digital display by ordering this a $2.64 part from digikey. http://rocky.digikey.com/scripts/ProductInfo.dll?Site=US&V=160&M=LTC-4727JR
Here is the manufacturer’s spec sheet for the display that was in my M-500.
http://www.liteon.com.tw/OPTO/SPEC/DATABOOK.NSF/PASN/DS30-2000-193/$file/C4727JR.pdf
If this all worked you could have a wideband that datalogs with a digital display for less than $300.
I take no responsibility if you wreck your wideband controller. I am just try to spread knowledge based on the observations I have made from my M-500. I have not verified any of the information about upgrading the M-200 through 300s.
I could take pictures on my board if anyone is interested before I put it back together.