A moderate repair costing in most cases $35 for treble strings (during a tuning visit), or ranging from $75 to $110 for treble strings (without a tuning visit). Single custom-made bass strings have an approximate replacement cost of $75 to $100.
Strings almost never break on newer or recently restrung pianos because new piano wire is extremely elastic. On older pianos, if the strings have become brittle with age, they are more likely to break—even if the change is tension is very slight. However, strings can and do break sometimes for no apparent reason at all. Should a plain steel string break during a tuning, we can usually replace it “on the spot.”
In the case of a broken bass string, which is a “wound string” (core steel wire with other wire—usually copper, sometimes steel—wrapped around it), if the broken string is still available, it is possible to splice the old string back into place. However, splicing a piano string is dependent upon the location of the actual break. That is, there must be enough core wire left to properly splice the string. If a bass string is missing, a new one can be ordered. However, each bass string on each make and model of piano is different. Ideally, the broken string is available to be duplicated. If it is not available, measurements can be taken from your piano for duplication.