My advice is keep the Walmart bike but put the widest set of these tires on it that will fit: Compass Tires. You will be very pleasantly surprised at the comfort level that supple tires run on low pressures can bring you.

Caution sales talk here(Take it with the appropriate amount of salt): "Supple tires are the most dramatic change you can make to the feel and performance of your bike. They roll more smoothly over the irregularities of the road surface, making them more comfortable and faster. They also absorb less energy as they deform with each tire revolution, which also increases your speed. Most of all, supple tires make your bike feel alive.

With supple tires, you can run wider tires at lower pressures, making your bike more comfortable and sure-footed, with no loss in performance. Professional racers have benefited from this research, but the bike industry continues to lag behind this trend and still reinforces most wide tires with puncture-proof belts and sturdy casings.

Our Compass tires provide the amazing ride of high-end tubular tires, but with the convenience of clinchers: There is no need to glue tires onto your rims any longer to experience the wonderful ride of supple tires. Thanks to their wider sections and lower pressures, Compass tires roll over debris that gets hammered into narrower tires, making them remarkably puncture-resistant. The tread is thick enough in the center to make our tires long-lasting. The tread pattern is designed to interlock with the road surface, so our tires offer amazing cornering grip, both in wet and dry conditions.

Compass tires are available in a variety of sizes to fit most bikes. Once you ride them, you won’t be able to go back to 'normal' tires!"

I suppose for comparison's sake you can consider this offer on CL in your area. You might like this if the frame is in your size and it's within your price range: https://pittsburgh.craigslist.org/bik/5627683107.html It seems like a pretty good deal.