I know this is an unpopular opinion, but don't assume a bike is junk because it's cheap and came in a box from amazon. There are a couple good ones out there. Be careful for sure -- but don't assume every cheap bike is junk.
I've ridden my $300 vilano shadow 4000 miles this year -- many of those miles through michigan winter.
The frame is heavy, but is tough and the weld quality is good. You also get fender/rack mounting points and tire clearance for at least 28mm tires.
While me and other vilano shadow owners have found that the tires and BB don't last particularly long (both needed replacement at around 1k miles), all other components are of good quality. Tires are consumables to begin with, and a cartridge square taper BB is cheap. No big deal. Outside of BB and tires, I'm running all original components.
Yes, you need to know how to assemble and tune various components, but all of this is very basic and easy to do. Information on how to do this is available online.
I am far from the only one, and every account I've read/watched online of this bike after many miles has been positive.