How much does it cost to replace/level a staircase?

My husband and I are looking into buying a house. We love the house, but the staircase leans to the right (previous owner added support beams for stabilization). I was curious as to how much it would cost to replace the staircase or if we'd be able to level the existing staircase. It's an older house with a ton of updates and it's priced right.