now see, for this, I would go with a wiki, and they are free...
Or ya, email it. You (or somebody else) are going to be spending a lot of time developing this app for a handful of people that might have a life cycle of 24 months, tops. Also, your gonna want a programmer that can to port security, with this app, your talking about sending data that can be hijacked across the net. Sure you run the risk everyday, but still man, It aint worth it. Go with an IM or email, that would be your cheapest, secure, most readily available solution.