Short answer: It depends on what you want and expect.
I'm using an old handheld GPS to give me ballpark position in LAT/LON to go with my paper charts as well as an indication of speed. I'm also using a fishfinder with the transducer set in a ball of wax to give me depth.
All together I'm into my electronics "suite" for around 200 bux, and expect it to last a few more years. If I want something more feature packed, it will require some serious spending on a 22 foot boat that could be put to better use elsewhere.