If it's original galvanized, then yes, it's probably on borrowed time. Would you consider doing it yourself? My first house's (1940s) piping sprung a leak. For some reason, the leak made the water taste awful, and I found it within a day thankfully. I got estimates of around $2500 to have it done. Instead, I spent maybe $300 on materials and took 2 day's paid vacation from work and did it myself. There's a bit of a learning curve to the knack, but once you have it down, it's a piece of cake.
On a slab or crawlspace? I had access to all pipes from the crawlspace. If you have to open up walls or go into the attic that could up the cost quite a bit, or give you more opportunities to pay yourself, depending on how you look at it.
How's your water pressure? Our pipes were really crusted up and the shower stream with the new pipes actually seemed painful till we got used to it.
