My advice is get the biggest unit you can, Lowrance makes a 8 inch screen for that price range, they also make a 7 for a bit less, lcx27/28(7 inch), lcx 37/38 (8 inch) (I think the model numbers are correct). I like my lowrance products. Hummingbird is also making some waves with their new units, but I know nothing about them. Honestly there are a ton of theads on here on the major units on the market right now, if you can narrow it down to a few you like I’m sure the search option will highlight the highs and lows of each unit, you’ll start to see some common things people like and don’t like by reading a few threads.
My very best advice if find a place that has them and check them out for yourself, Gander Mountain, Cabela’s usually both have a large selection on hand to play with, though I’m intrigued myself with the new hummingbirds, I still don’t like something about them, the buttons the display, something just doesn’t do it for me, but I suppose that’s more of a personal issue, you may find the same, or it may not be an issue.
Install wise I don’t think you need much more than a couple hours to do it, I suppose it all depends on how you want to install it, I ram mounted mine, I’m pretty sure even with all the messing around I did with my installs it didn’t take me more than a couple hours. I was going slow, being careful, triple checking everything, and the install looks great and I didn’t have a single problem. Nothing really hard or technical, just takes a little time to strip the wires for the power cord, and run cables through the boat, and I suppose it depends a little how you want to run your transducer, I ended up mounting a plate on the back of my boat so I could change transducers without redrilling into my boat. I also pulled a transducer extension cable through my boat so incase I have to get a new transducer down the road I can just hook up a new one and not worry about pulling the cable through again.