I worked in a department store in the early to mid 1980s, and our photofinishing supplier gave our customers 24 hour turn-around during the week - basically so we could compete with the mini-labs.
They were cheap, and reasonably competent, even if pro-lab user me would sometimes grimace a bit when I reviewed the results with the customers.
As far as film sales, there were probably three leaders.
1) pre-paid processing Kodachrome at $11.99 CDN IIRC. We were a Kodak pickup and delivery dealer, so we had 24 hour turn-around on Kodak processing during the week on this as well;
2) the normal variety in emulsions and formats of Kodak amateur films that one might find at a busy camera/film department in a busy store in a big, busy Canadian city. I have no clear memory of those prices, but $5 or less wouldn't surprise me; and
3) house brand print film (mostly) that was actually made for the department store chain by 3M/GAF/Ferrania. It was very inexpensively priced - about 2/3 of the Kodak prices, IIRC.
Most people who tried out the house brand film eventually switched to Kodak. If you saw the prints made from it by our photofinisher, you would understand why. I never recommended it.
We also sold some Polaroid SX-70 film, plus some Ektachrome. I can't remember ever having any black and white film available, but we might have. We also sold some truly awful house brand or GAF branded E6 processing slide film.
Most of the film was displayed in a wall of film behind the main counter, and we were constantly having to replenish that wall from the boxes and boxes of inventory that arrived frequently in the back room.
A wall that looked a bit like the old setup at Beau Photo in Vancouver, seen here:
It was all part of the Kodak ecosystem that, by its zenith, "manufacture(d) upwards of 70 master stockrolls a day of Kodacolor…each and every day – enough to make nearly 3.4 million spools each day".
The remnants of that ecosystem is what Eastman Kodak is today, and their master rolls - the minimum volume they can economically and practically make - are probably still enough to make nearly 50,000 individual still rolls of film.
It wouldn't surprise me if our absolutely ordinary and unremarkable camera and film department - far from a major player at the time - sold more film back then then B&H, Freestyle or any of the major retail sellers. Certainly more than Amazon.