Should be able to find a good Humminbird 170 and Lowrance X-4 new for under $100, or some slightly better models on eBAY for less.
Note, I would recommend buying second hand, but make sure to check condition of the connectors and if possible one that was used in fresh water.
I have a lowrance x-4 DSI Unit and it uses a small 12v battery that goes in the hatch. You can probably find a similar unit for under $100. Only had to drill one hole in my hobie for the transducer cable. Overall a really great kayak friendly unit, just the price Is kinda high.
WalFart has the Humminbird PiranhaMAX 150 for $79, the 160 for $89, the 170 for $99 and the Lowrance X-4 for $79. All three can be powered with 8AA rechargable batteries.
I've had both the PiranhaMax 160 & 170 and they can't be beat for the money....all the above would work for your Necky.
This is the P160 (right side) mounted on a Ocean Kayak Prowler 13-
8AA rechargeables in a WalFart waterproof box.
Last edited by Lt.FireDog; 04-25-2012 at 06:47 PM.