I've got a Humminbird 898 and absolutely love it. It is well worth the extra money. I don't use the down imaging that much. But the side imaging has honestly helped me catch a ton more fish.
I also like the "buying used" suggestion, if you're on a budget. Search ebay and such and you should be able to find a quality unit.
I'm waiting for Johnson Outdoors (Humminbird/Minnkota parent company) to come out with a link up, so I can send waypoints to my Terrova I-Pilot from my 898. Wishful thinking maybe