For casual riding you can get pretty much any bike you want, at any budget. My first road bike was only $150, with friction shifters, but it was perfectly adequate for long rides over varying terrain. I completed my first century ride on this bike, with no issues at all.

The important things are to get a bike which fits, and to set it up properly. There are plenty of resources online which can advise you of the proper frame size, and a good bike shop can get you fit reasonably close.

For casual riding, I would not waste money on a new bike. There are garages across America with nearly-new bikes hanging from the rafters, ridden a few times, then left to gather dust. If you find you like riding enough to put in a lot of miles on an older bike, you can honestly justify spending more, later, on a new bike.

Many people, especially on this forum, are into the latest and greatest when it comes to bikes and components, and these tend to be expensive. For all-around riding, you can easily find a decent bike for under $200. A look on the local Craigslist in my area shows at least a dozen bikes under $200 which would be good enough for the kind of riding you are talking about. If you shop around, you can get a good deal on one of those "nearly-new" bikes sleeping in someones garage.

Brands are not important, any mainstream brand (Specialized, Trek, Bridgestone, etc) are good enough. So long as it is the right size, and nothing is cracked or broken, the brand is irrelevant.