https://www.thespruce.com/basic-types-of-pl...g-pipes-1822487

Not sure of the local pricing plus labour.

Generally most plumbers will recommend replacement of the entire piping unless he can try to detect the leak without a guarantee that it is the spot. You have to take risk as every job is different. Depends whether he wants to put in the extra effort.

Two months ago  I notice the drain outside my house is alway wet even on a hot day. Did some investigation and found that the elbow was leaking.

DIY a bypass using the same material and problem solved. Dont have to use high grade replacement pipe for a small section. Some high profile 'plumber' think that only high grade can solve a problem.

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Sorry no plumber to intro as most my house things I diy unless is major.

If can identify the leak spot, then normally is just replacing the area.

Not many would want to do the entire house piping unless is no choice, if is a very old property.

Is not just replacing from the main to the reserved tank but also from the reserve tank to the the various bathrooms for a complete overhaul of the entire system.