The budget really restricts you here to old bikes second-hand, or brand new junk bikes. I'd avoid the latter.
Since it's the budget that's restricting you, I wouldn't worry at this point about the type of bike. Lots of people commute on MTBs, hybrids, road or cross bikes. Anything in the price range that fits, works reasonably well, and has the potential for a rack and fenders, should get serious consideration. You may have to wait for the right bike to come along, depending on the second-hand bike market where you live.
Where I live, the $100-$300 range is dominated by 10-15 year old entry-level mountain bikes, with 20-30 year old road bikes coming in a close second. Scanning Craigslist a couple of times a day, it was still over six months before I found a decent contemporary road bike in that price range. I bought it the very afternoon it was first listed. It was mid-January, BTW, and the guy said he had a dozen emails after he'd commuted to my no-questions-asked commitment to buy immediately. He pulled the ad within two hours of posting it because he had so many offers.
In other words, at least where I live, it's not casual browsing, but an active, yet patient search that will yield success.
Back to the Wal-bikes, you might be able to make one work if you can fix any assembly mistakes when you get home. And you understand it's designed for the type of person who will ride it a couple of miles a half-dozen times before permanently garaging it. Therefore, the components don't need to be very durable, so they aren't.
The guy who really inspired me to return to cycling was a huge fan of Wal-bikes. But he also knew their limits and was prepared to replace them two or three times a year, at the first sign of trouble. Which he did. He always seemed to have new bike, and never paid more than $79 for one (ten years ago). It made him happy, so no harm, I guess. It's just not the kind of choice most of us make around BikeForums.