As a lifelong near daily rider, I offer the following.
For the most part, big box retailers do not sell good bikes, they pretty much sell cheap and/or bottom of the line throw away bikes priced for the masses, and yes, very unlikely that there are any actual bike mechanics that assemble and set the bikes up and many of the big box bikes are so bad, they cannot be adjusted to function nicely. You are far better off buying bikes from an actual bicycle shop.
For average to medium use riders, once you pass the $300+ price point you will be getting a good quality bike. Most manufacturers such as Trek, Specialized, etc., will offer a similarly outfitted bike at similar price points.
Going with a name brand you can pretty much assure a comparable bike at a given price point. From a riders perspective, there is far more of a ride quality difference between say a $100 and a $400 bike than there is between a $400 and a $4000 bike. If you do not intend to ride distance everyday, don't spend more than $400 initially. If you become a daily distance rider, you will appreciate the bike you get for $1,200. Anything beyond this is a largely a waste of money unless you are a competition racer, serious off-roader, or just want to display that you have money.
Since kids will quickly outgrow a given size bike, this may be good reason to find a good used bike and or a throw-away hand me down. Blackstone Bikes may have some decent bikes for the money. A good quality used bike is a much better purchase than a crappy new one.
Bruce.