Just for another point of view, my price for an 18' X 36' Liner replacement is around $3000-$3500 CAD. This price includes 4 hours for my crew to repair and clean the bottom of the pool and saving the water in 2 of our quick-set pools. The price of $2500 for the stairs is not bad either. But like Waste said, whoever is doing it should have experience with liners over steps. They can be extremely tricky.
I would also agree with the idea that the first guy might be pricing the plumbing part of the job a bit high because he might not want to do the job. I would definitly get a few more prices.

Brad