Foundation repair – Allied Foundation

I recently had allied foundation come out to give me a quote. I'm the newer homeowner to this house but it previously had foundation work from this company so that's why I called them back out. Since I bought my home last March, my home has developed some diagonal cracks around windows and we've started having doors that are sticking. Google says those are signs the foundation has shifted.

I had 2 other companies come out and 1 other company basically agreed with Allied's assessment of where new piers need to go. My quotes were $7000 (7 piers and deviated the most from what other 2 companies said), $6000 (6 piers and independently agreed with allied's assessment but suggested more piers), and $700 with Allied being the cheapest by a long shot at $700 for 2 new piers and adjusting 2 old ones. What am I missing here? Why are they so cheap? Is the cost of materials just that cheap?

For background, I've had the hardest time just trying to get them to call me back after the walk through. The guy that came to do my measurements during the walk through gave me no details whatsoever and I basically had to call the office and have one of their office people tell me what I needed but I can't deny the fact that the other 2 companies pretty much said there were no issues with where most of the original piers were set. Help me understand here.