I think the place to start is figuring out what sort of riding you want to be doing. There are road bikes, mountain bikes, and the in between that are typically known as "comfort bikes". I'd probably recommend the comforts for ya. They're a more upright ride, have things like shocks and more cushy seats, and fall about in that price range. They're not the fastest on the road, not the best on the trail, but they usually can take you anywhere at a bit slower of a speed.
I've been incredibly happy with my Cannondale touring rig, and they offer a comfort bike for $449.99.
http://www.rei.com/product/763296 Giant also makes pretty good comforts for $440.00, the Cypress, geared more to road riding, and the Sedona, geared more to trail riding.
http://www.giant-bicycles.com/en-US/bikes/lifestyle/
However, don't just go based on my word. The most important part of a bike is how it fits you. Head to a real bike shop, tell them what you want, and, if they're worth anything they'll give you a couple suggestions and size you up for bikes. They'll adjust the seat and handlebars to where they should be for you, and let you ride it around outside or on an indoor trainer to be sure that it fits you correctly.
Nothing is worse than a bike that doesn't fit properly. It leads to tired legs, arms, and back.
Best of luck looking, and safe riding. Let us know how it works out
