you don't have to have SI
for example: the Helix comes in different configurations, with or without side scan and in your price range...
recommend the largest screen you can swing
allow around $100 or so for a map card
your going to want SD cards and readers so you can load updated software to your machine, and back up your waypoints, etc..... just don't buy the cards and reader sold by the mfg of your machine... go to Best Buy or some other source for those things, and you can get those things much much cheaper...
get a couple cards so you have on for backups and one for software update
sale electronics at Cabela's.. other places will be closing out items to make room for the new models
...I use Humminbird, have 898csi and 998csi... like them a lot
have heard real good things about the Helix from a friend, the 5 and 7 are in your range
Another thought on this is if you have a smart phone you can install the Navionics App and use that as your GPS. Then pick up a basic non-GPS locator. If you ice fish you have the stuff on your phone to use as a map as well so it's pretty handy for someone who doesn't want to or simply can't fork over a bunch of money for a combo unit.
Keep your eyes out on various fishing sites besides this one. Guys will be selling their used locators and you can find some pretty decent deals on them....or check places like ebay or craigslist. They pop up on there all the time.