If you decide to go with a lowrance touch unit you could get it with an HDI transducer and that would give you 2d and downscan with only one transducer on the trolling motor. You would also be able to link it to another unit later.
There are also some rebates available on the Gen2 touch units right now. I just bought a Touch9 and a Point1 antenna and got a $300.00 rebate on the pair. I'd definitely check with Brian at BBG Before you buy.