Do not ever buy a bicycle from Walmart or any department store for that matter.
They are called Bike Shaped Objects (B.S.O.) for a reason.
If anything buy a used bicycle, preferably steel. I like old Rocky Mountains and Specialized bicycles, then I upgrade the shifters, levers etc over time as I can afford it.
I have bought a BMC geared motor for $20 laced and ready to go, but the gears were stripped and I replaced them. Controllers are cheap, $25 on ebay, throttle on ebay $10, but here is the kicker, the battery. Do you want some unknown quality battery built in some China-mans basement? I wouldnt. You can go to Home Depot and buy the EGO battery pack for $60/Ah plus the charger is $75 (CAD), you could buy authentic cells and build your own, if you are going to solder then buy them with tabs on. NKON does that for you. Bicycle you can find for free, I know a few bums who always find bikes. Online classifieds you can find a bike for $25 or $50 and up.
I bought a department store steel ebike used, for $200(CDN) but the lead acid batteries were toast. I burnt out the brushed geared motor in no time. The frame though is what I wanted.