You don't need an expensive bike, but don't cheap out, either.
A Walmart brand will be adequate, but you really ought to upgrade if you are going to ride at all. The difference in a good bike and the Walmart ones is astounding, and you'll feel it on the first ride. And you'll be much more likely to stay with it.
I have the bike linked below. I think it's called a "comfort bike". It has a fatter seat, upright handlebars, and fatter tires. Not as capable as a mountain bike, but great for rough streets and flat dirt trails. I've ridden as far as 30 miles on pavement. Mone was $600, these are listed at $700. You can also get a step through, which would make it easier to "walk" as mentioned above.
https://www.specialized.com/us/en/rollI also have recumbent trikes, which are a blast to ride, and get a lot of attention. The drawback is they won't fit on mountain bike trails, and they are generally expensive. I've bought a Terratrike Rover for $500 used, when new price was $1500. Also found a better TT for $500 that was $2500 new.
The best brand is Catrike, which run $4000 and up, I haven't found one used for a price I wanted yet.