Tires are the most important, much more important than frame and fork material when it comes to comfort, especially on rough pavement, gravel, etc. Carbon, steel, aluminum - they make excellent, comfortable bikes. Don't worry about materials. All work very well as long as you get it to fit, get a saddle and handlebars you're comfortable with, and don't use skinny tires unless you really want to lose that extra minute on your commute.
I have been riding a cross bike turned commuter for a year and am really sold on that type of bike for commuting and most recreational use. They can be as racy as you want them to be, but are also equipped from the get-go to take 32+mm tires which are great for commuting. I use smooth tread tires rather than knobbies, and if you want to do winter commuting, they make a variety of studded winter tires so you can do that too. Many, but not all come with eyelets for fenders and rear rack - make sure you check on that.
You can set up most cross bikes as full-on commuters or touring bikes with rear racks, maybe even front racks, fenders and nice wide-ish tires. You can set them up to very closely mimic a "real" road bike by just taking off the extra stuff and putting 23's or 25's tires on it. If I had one bike, it would be a cross bike with two sets of wheels (light and skinny and heavier and wider).
Although I love my carbon fiber road bike, my aluminum cross bike is very fun to ride and very comfortable. With fenders, rack and 32mm tires, it isn't as light or fast as my road bike, but for much of the riding I do, it's actually more fun to ride, and actually is faster in a lot of conditions - on the crappy bike paths, gravel strewn shoulders, etc. I know it's a lot faster on horrible the gravel roads that make up part of my commute.
Go to your favorite Fairbanks bike shop, the one you feel most comfortable with, and talk to them about your budget and uses. Don't worry about frame material- that can be debated all day. But in that price range, and paying attention to fit and tires, you won't get a bad bike.