Cost of renovating a too small bathroom?

We're house hunting and found the perfect house, but the master bathroom is very small. It has a small stand-in shower and 1 small sink. We're wondering if it's worth getting and renovating, so how much would it cost to knock down part of the wall, convert the stand-in shower to more of a tub/shower size (without moving the plumbing etc.), maybe adding 1 more sink, and building a wall around the new facility?