Hi Mary
There's a few things you can do, the first of which I'd absolutely say get a home buyer's warranty. American Home Shield has a great one. Essentially, it's another "insurance policy" that covers your major appliances, plumbing, and electric. Before you run away, is the plumbing actively leaking? Have you gotten a quote on the cost to replumb the home? Are the sellers willing to contribute to repairs and if not, are you getting such a significant savings on the home, does it behoove you to consider the deal you're getting is worth a potential repair down the road? You are able to renew your home warranty every year-they're about $1 a day.
Was this disclosed on the seller's disclosure? If not, that's a pretty big deal. If you're not working with a Realtor to help you purchase, it may be hard to negotiate half or all of a replumb, but if you do have an agent-they should be able to help you work something out. Afterall, you're a buyer...you hold a lot of the cards. And, the fact is, now that the sellers are aware of the plumbing issue, they do have to disclose it for other buyers if your contract falls through and, they will more than likely have to either sell for less or repair it anyways. Be tough, but fair, that's what I always say.
Your Favorite Realtor,
Amanda Sarnes

I have seen this product in brand new homes in the Sacramento CA area.
I am not that familiar with it.
Call some local plumbing contractors in your area and get estimates to repipe the home with copper, and then take those estimates into the negotiating process.

I had my house re-piped for the same reason in 2003. It's a 1,480 square foot home and it cost $3,100 to re-pipe it with flexible pipe called PEX. If I had it to do over again, I would have investigated PEX and probably upgraded to some kind of metal pipe if possible. I'm concerned about possible safety hazards with the PEX. Because the re-pipe had to go through the attic, the water in the pipes heats up and the water coming out of the faucet tastes just like water from a garden hose. That taste was fun once in awhile on a hot outdoor day as a kid, but not on a daily basis. I have to buy bottled water because of it. I hope that helps you.

Dear Mary

As A Florida Home Inspector I see this in alot of older trailers. I have seen it first hand blow up and cause leaks and flooding. You should ask the seller to pay for the repairs of upgrade. Im sure one of the owners in the past got the money out of the law suit. Every home that had it was signed up. I knew a team the covered florida getting every home signed up and paid. So where did the repair money go is the question. If it can be crawled under good it should not cost that much to do the whole home. Im sure you have already bought this home or moved away from it by now.
Good Luck

Mary
I would get a bid on having the home re-plumbed and take it to the sellers. Anyone else is going to ask the same thing.
Keith

I am the owner of 2 4-plexs with Polybutylene Plumbing ... a recent flood inside one of the walls not only flooded all four units but reveled mold issues from previous leaks ... run away!!!