Having just purchased a gigalog E datalogger for about 260 euros, I would very much welcome a cheaper version. The sort of stuff I need to log is GPS signals along side, side scan sonar and metal detector signals.
Having never used a datalogger, the PDF manual I have could have been far better. There are too many abbreviations and a lack of clarity. If you are going to aim for a wider market then the manual will be all important.
If you have the time, one question, If you are logging a signal from a headphone feed, there are three wires, left and right channel plus the ground. I take it only one of the channels needs logging, but does the ground wire need connecting? 