I love gadgets, so I couldn't resist taking a look at what was possible.
I am new, so tragically I had to take all the links out of my post! So you will just have to take this research on faith.
A quick Google search revealed that you can buy a NASA AIS black box receiver for $200. I have to admit, the NASA brand made me wary - this product was not made by the US space agency! At any rate, you get an AIS receiver that will hook up to a PC and the included software automatically plots the AIS returns. You can also hook up a GPS receiver to it and then it will plot your own position as well.
Seems like a pretty cool idea and the price is very affordable.
The device Dieselboy found on eBay was the same company but with an included display. It's cheaper from Cactusmarine.com (where I found the other device) than the eBay vendor. To be honest the display looked poor and so I think I'd seriously consider the PC-based version.
I'm an Apple loyalist, personally, but with manufacturers practically giving away laptops in cereal boxes nowadays there's no reason not to buy a cheap PC laptop to use with this, and the total cost would be little more than the model with the lousy built-in display. Of course the PC wouldn't be ruggedized but you can't have everything ...
Of course none of this solves the original poster's dilemma of how to spot vessels with radar but without AIS. The diagram with the CARD system might give a clue as to why it was discontinued - it shows that the likely range for radar detection is only about 6-8 miles, and that might not give you enough time to successfully wake up and avoid a large, fast ship or sport fishing boat.
I couldn't help but think it would be pretty cool to have an AIS transmitter and to therefore stand tall and even with these really expensive ships. The Nauticast B AIS looks like a nice start for $729. You have to get an ID number from the FCC if you want to cruise internationally and that appears to cost another $160. The procedure appeared very customer unfriendly and it would take a phone call or two to the FCC to make sure I understood it.
So there are a lot of very interesting options for AIS, one for pretty much every purse and purpose. I'm disappointed AIS transmitters are so expensive and that the required licensing (for international cruising, anyway) is too.
The good news is that sportfisherman our original poster talked about with the new 70' Bertram probably will have an AIS transceiver in a few years just because it will tickle his ego to be with the big boys. Once AIS transmitters cost $199 I'm sure we will all have them. As long as the FCC can be a little more reasonable about licensing ...