That's a tight budget, but take a look at the HB Helix 7 CHIRP DI GPS G2N. It has DI, but not SI. If you step up in rice to around $700 you can get the Helix 7 with SI and DI.
Helix is very user friendly. You don't have to be an electrical engineer to operate it. Garmin and Lowrance just aren't as good as HB.
Capt. Craig Copeland
Licensed by the US Coast Guard
2013 Nautic Star 2110 Shallow Bay Boat
Humminbird HELIX 12 CHIRP MEGA SI GPS G2N
Nautic Star Boats Pro Staff (nauticstarboats.com)
Redneck Fish'n Jigs Pro Staff (redneckfishn.com)