chaseh200 - if you are searching for brush piles, submerged timber, etc., you will want side and down imaging. Almost everyone will tell you - buy as much as your budget will allow. Size of screen and the density of the picture will help identify if your new found structure has fish on it. You might want a lake map, but isn't critical for your intended purpose. They aren't cheap and you might find used. I haven't used it but understand you can get a $15/year subscription to Navionics to use on your phone, which would require internet connection on the lake.
Another option to keep in mind. Many upgrade their electronics regularly and you might find a deal on a higher end unit.
I highly recommend the following approach:
Find some units that are in your price range that you are interested in. You can do this by looking online or going into stores like bass pro.
Use Youtube for demonstrations/reviews of some units you are interested in - there will be a lot of information there to help you decide and see features, how easy to use, screenshots, etc.
Also, look in the trade forum here and if you see something that is a little higher end, used and in your price range - repeat the Youtube research, check with the seller on condition, etc. You won't have warranty, but you might get a unit that has a little better function for your use
When you install it. Make sure you either have it done, or do some research here too. Isolation from interference, where to mount the transducer, wiring, etc. all matters in reducing noise on the display and how effective it is for you.
This sounds a little complicated, but following this will make you happier with the result.
I use Humminbirds but based on Tin Boat's response, found the next size up Hook2 9 is on sale @ Bass Pro for $499 and includes detailed maps for 3000 US lakes so you might not need a map card which would be an extra cost for you. Hook2 9 at Bass Pro