When I had my roof done, I got three quotes; two were within ~$300 of each other; the third was ~$3K more. And they were all quoting the exact same job and materials. I was shocked that two bids were so close to each other. What's funny is the two businesses that gave the almost identical quotes were "old school"; two guys came out with a tape measure, were up on the roof for 10 minutes, climbed down, and 5 minutes later gave me the quotes hand-written on a piece of paper- tear off, ridge vent, felt paper, 30 yr shingles (my choice of manufacturer), etc. The third place that was so much higher took a few days to finish the quote. They did this really detailed quote itemizing everything, it was printed out... funny in comparison. I guess they were paying for that computer.
I gave the job to the middle bidder, I liked him better, and he did it for the same price as the low bidder. I gave them a few days' notice for when I wanted it done- no rain, and they showed up that day. They had a 4 man crew, plus the owner on the ground helping, and were done in a day. Did a nice job, no complaints.
In my area, I was surprised how few legit roofers there were at that time- it seems that they're like tree services and go out of business every 5 years. The two guys that gave nearly identical quotes have been in business for 20+ years.
Yes, apparently shingles have really gone up in price over the last few years. Same with lumber. The guy that said that his roofing quote went up 50% in a year said that it was almost all due to material costs increasing.