You can occasionally find a good set of Motorola T-1504 Pass/Reject duplexers for the $100 - 150 range on ebay. They work quite well. Mine are giving me better than 90 db of isolation on my 440 repeater, and allows me to run a 18 db preamp on it, while running 30-watts with not a whisper of overload.
But that's just my 2 cents
73s ~ Bill, n1rik