You should really get a dual-channel RX since You want to use it for
navigation. You will get updates twice as often, which is very important
considering the new ClassB trasponders for smaller vessels only transmit
positions every 30 seconds. That means only every minute if You only have
one channel. I promise You, in that last minute You will want to know who
is turning where...

I can recommend the SR162, also available from Milltech at $439. The SR
series are made by a Chinese manufacturer but with engineering help from a
Swedish team of AIS engineers which has improved the product a lot.

The new ClassB transponders are not yet FCC approved but are available in
Europe for around $1200.

/Marcus