I'd buy a used '90's steel-framed mountain bike with no suspension. Maybe a Trek 820 or something. Spend about $50-$80 on the bike. Then get slick tires for it, a tire patch kit, a pump, maybe front and rear LED lights, a good lock and a helmet. Have a bike mechanic go through it for lubrication, cabling, etc. You'll probably exceed the $200 budget unless you can do your own wrenching at the local bike co-op, but this would be a good commuting rig, and serviceable for decades to come. Not so much the Walmart bike- they usually only last a few rides before needing major surgery.