If you are looking for a cheap and simple AIS receiver for your PC chart plotter the NASA AIS Engine might be a good alternative.
I am going to order it and check it out. But as far as I understand from the bloggosphere and Google it seems to do the trick. It receives on both A and B-AIS-channels by switching – simultaneous would have been better, as a ship might sneak up while the NASA engine is busy listening on the other channel. It also seems to work well with the PC-navigators. And the price is more or less 100 – 120 Pounds in the UK.
I talked with the designer and owner of the Norwegian Tiki Navigator, who is certain the software – the navigator with AIS-integration – will be commercial available within march.
This link is a blogger who seems to have tested the NASA AIS Engine as thorough as can be expected. It ia well worth checking out.