After having my first deal fall apart due to foundation issues - I can say it varies tremendously.
Just for an example - when I put the above mentioned house under contract, the seller had a quote for ~$6k. Okay, sounds good. Had a structural engineer come out, and he says the house is verging on structural failure - needs 3x as many piers as the original quote, including the entire interior of the house. Had two reputable 20+ yr companies bid ~$25k, with high risk for other damage occurring during the job (plumbing, brick, roof, etc.)
I have seen price quotes range from $200-$600 per pier, depending on type, quality, etc.
Turns out the original foundation quote came from a company only in the business for 3 years, giving lowball bids with supbar materials and little to no experience.
I would suggest having a licensed engineer look at it and give his recommendation, the $400 it costs could save you thousands in the long run. Also, have an experienced company do the work - lifetime warranties are worthless if the company is gonna be out of business in four years.
Sorry for the long reply, hope it was at least somewhat useful.