I'd just hit up whatever bicycle store is nearest to you! If you're just looking to do occasional riding, go for a "hyrid" -- slightly thicker tires than a skinny-tired racing bike, and slightly heavier, but not too heavy.

I don't know what the pricing will be like in your neck of the woods, but in the bike shops near me here in NYC, you can get a nice new hybrid for about $300 to $450. I bought one for about $400 in 2010 and it's been great.