Joined: May 2007
Posts: 3,798
Likes: 1
From: Highland Park, NJ, USA
Bikes: "Hildy", a Novara Randonee touring bike; a 16-speed Bike Friday Tikit; and a Specialized Stumpjumper frame-based built-up MTB, now serving as the kid-carrier, grocery-getter.
In general, touring bikes make excellent commuting bikes. They're also out of your current price range.
$400 is barely doable in this price range if you find an old hardtail mountain bike and build that up with racks and barends. (Not as gooed as drops, but miles better than flat bars alone.) Loaded touring (i.e., camping) would be touch-and-go on a setup like this, since you will want heavy-duty racks and decent panniers to support the weight of camping gear. Make sure you get something that can mount a rack.
There are probably hundreds of threads around about MTB to touring bike conversions.
However, that said... you can tour or commute on pretty much any bike, it's just a matter of how comfortable you'll be. You can always get a clunker now and a save up for a better bike. this has the advantage of giving you riding experience so you'll have a better idea of what you need.