Look for Kinesis AC210, Goldtouch gtc0033/0077, and Genovation. You can usually find one of those on ebay for less than $40 and they all have MX. The Genovations are programmable, so those would be my first choice. The usb ones are usually a little more though. There is also the Adesso AKP-220B with MX, but it's build quality isn't super. Of course the Cherry G80-3700 is a good one too, but is usually a bit harder to find and/or more expensive.