Bicycle recommendation?

I'm a 6'5" male and weigh around 310 pounds. I'm looking to occasionally do some weekend leisure biking--almost entirely on paved surfaces. Since I don't plan on biking much I don't want to spend "a lot" of money. Should I pick up like a Walmart bike or should I go to a bike shop? Also, as a hypothetical, if you had to choose a brand without being able to see or try-out any particular bike which single brand would you choose for my situation described above? Thanks!!