TLDR version: "Big Box Store" bikes are not a metric for what a bicycle "costs", and cheap bicycles have high operating expenditures. Why not spend more on capital expenditures (the purchase), take less trips to the bike store for repairs, and have a nicer bicycle to boot?
BBSBs are the bane of every bike mechanic, because 1)their owners have extremely unrealistic expectations in terms of cost of labor and parts (ie: "I paid $75 for this thing, you want $50 to replace this whosamahwhasis?") 2)the components are almost never standard (so parts are not normally stocked, or may not even be available) 3)Everything, and I mean everything, is as cheap as can be, and falls apart, so they're 'frequent fliers.' The cables and housings are weak and made of poor, incompatible metals so they stretch making proper adjustment difficult, and corrode the second water even comes near them. The bearings are poorly sealed (ditto on water) and substandard (so they fail quickly.)
I know shops that pretty much point-blank refuse to even work on such bikes. Just the overhead of all the extra time explaining to the customer why they have to pay "so much" sometimes puts a shop into the red on that particular transaction.
The bicycle industry is full of competition. There are three major component manufacturers, dozens of frame builders, and more than three major distributors of parts and bikes in the US. In my city I can name about twelve bicycle shops within a 4 mile radius of me, and each one of them stocks at least half a dozen brands. If you think the bike industry is a "ripoff", then by all means, start your own component, framebuilding, distributor, or retail business and "do everyone else in."
The problem is that bicycles are considered toys, and as such: people pump $60 of gas into the tank of their car that they're paying $400/month for a loan plus at least $100/month to insure....and then go to the local bike store and whine and bitch and moan about the price tag on a $400 bicycle that will last them years of commuting...