Foundation repair is priced by the unit of work, not by the size of your house, which is why two homes on the same street can get quotes that differ by a factor of ten.
How the Pricing Is Built
Pier work is priced per pier. The number needed depends on the length of footing that has to be supported and the spacing the job calls for. Supporting one settled corner is a small job. Underpinning two full walls is not.
Crawl space support is priced by the number of new footings and posts, and typically costs a fraction of perimeter piering. This is worth knowing because a great many Birmingham homes with sloping floors need interior support rather than underpinning, and the difference in price is substantial.
Encapsulation is priced mostly by square footage, adjusted for water management and any framing repairs needed first.
Drainage is priced by linear foot, plus the sump and its discharge.
What Pushes It Up
Low crawl space clearance, because working in eighteen inches costs more than working in four feet. Difficult access that rules out larger equipment. Greater depth to competent soil than expected. Standing water that has to be dealt with before anything else. Rotten or termite-damaged framing that has to be replaced before it can be supported.
What Is Usually Excluded
Cosmetic repair, almost always. Piers stop the movement, but patching drywall, repointing brick, re-hanging doors and replacing cracked tile are generally separate or not included. Check this explicitly on every quote, because it is the most common source of unpleasant surprise.
Comparing Quotes
Ask every contractor the same three questions: how many piers or posts and of what type, whether the price stabilizes or lifts, and what is excluded.
Then ask what happens if you do nothing for twelve months. A contractor who answers that calmly and specifically is diagnosing your house. One who cannot is selling you something.
Free inspections are standard in this trade, and they are sales visits. That is not sinister, but the person assessing your house also sells the repair, so a second opinion on anything significant is worth the time it costs.