(1) If the metal pipe is actually a LEAD pipe, you would be well advised to replace the whole lot without delay with either a copper pipe (unless you have a really agressive soil) or a polyethylene pipe. This may be insulting your intelligence but lead is toxic and you would not want to be getting your drinking water supply via a lead pipe.
(2) The pipe could be GB - gunbarrell (steel) or copper. If it is copper the simplest way is to cut out the affected section and replace with a short section of new pipe of the same diameter and same material (i.e.copper) using 2 No. 310 (straight connectors) compression fittings. If it's GB the chances are the whole pipe is corroded and any cheap quick fix job done on it now will be a false economy. You would be better off replacing the lot.
Part of the high cost of replacement may be due to having to dig up your garden or driveway. If so, this can be avoided or reduced by using moling. This trenchless technique allows a small diameter pipe to be run into your property without digging a trench and could result in a major saving. The Gas Company use it extensively.
One assumes that you are not paying any water charges because if you were metered you wouldn't be so worried about the cost of the repair! Also that leak is :
(a) reducing pressure to your property.
(b) possibly underming the foundations of your property.
(c) wasting an increasingly precious resource.
J
March 2008