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the best cheap bikes from wallmart, are the most mechanically simple ones. So no suspension or disc brakes. I just had a look online and it's the ones in pic related.
Just be aware that these bikes will be setup by absolute retards and have parts that are only in theory adjustable. So the bearings in the hubs will need servicing out of the box to run properly. The drivetrains will probably not shift flawlessly. The brakes will warrant pad upgrades, possibly re-cabling and definately adjustment. Like it's probably going to be rideable on a basic level but warrant some attention.
You're in for a similiar amount of effort and learningn how a bicycle works as you would with a used bike. And they're gonna be destined for the trash after a couple years. But still, even an absolute shitter bike is still a bike. If you have no other choice go for it.
Your better option by far, if you have a good local market, is to buy a bike off craigslist. If you're prepared to do that, post your local craigslist I can make you some recs. And if you buy a wallmart shitter please post your experiences with it, because i'm curious.