I'll second LastPlace's recommendation on the Codas, though I believe the basic model Coda is 450, which may be pushing your price range. I think you'll like the Codas however as they will feel nice and fast, but the steel frame will be durable and with the right tires you can easily take it off road, as long as it isn't intense singletrack or something. Kona also makes great bikes. The Kona Smoke would be a great starter bike, and it already comes with fenders. For a little bit more you could get a Kona Dew, which will be fairly similar to the Smoke, but with slightly better parts. If you come down to deciding between the Coda and the Dew, for instance, the Coda will be a little better on the roads and the Dew will be better off-road.
Used can also be nice, but for a beginner, there are a lot of advantages in buying new: free fittings, the bike should be tuned up nicely, andd it's a place you can easily go for advice on maintenance.
Good luck! : )