here is a hummingbird 363 for 300 bucks. it will give you water depth, speed over ground, anchor alarm IIRC, a look at the bottom, and basic chart functions. it is black and white with a 4 inch screen, while not huge it will do what you are looking for. as for the transducer you should be able to either use epoxy or a wax toliet ring to "glue" it down some where in the hull that works
after i get an auto pilot it is what i plan on getting