for street riding you dont want something with suspension and you want something with more that 7 gears.
Three to five gears are plenty. Most city bikes come with maintenance-free hub transmissions.
These bikes also come with sufficiently wide and thick tires, that suspension is a non-issue at normal speeds.
As most have said, a used one will run you less than 50$.
In most of Europe you can usually get them for less at the local Police auctions, where lost/stolen bikes are auctioned off, if they aren't collected by the owner.
Since there are less bikes in the States, I suspect they may be slightly more expensive, but just get one that is mechanically sound and safe.
Working brakes (good pads, adjustable screws, well-soldered terminators on the pulleys, which don't rip off when you use the lever) are important, and straight wheels are the difference between a good deal, and a worthless bike.
If there's still some profile on the tire, and they're not flat spotted, that's great too. Lighting is nice to have, but also easy to replace with stick-ons.
The foldable one looks nice too, but I somehow can't trust collapsible frames. And a new bike should come with proper lighting.