Does lying invalidate good deeds, and is a Muslim considered a liar for a single lie, or is there a limit to that? And are the sins of lying forgiven by saying "Subhan Allah wa bihamdih" a hundred times?

Lying is abhorrent. The basic principle is that it does not nullify good deeds unless it is a means to major hypocrisy. Major hypocrisy is the outward show of faith while concealing disbelief, whereas minor hypocrisy (hypocrisy of action) is the outward show of righteousness while concealing its opposite, and its foundation is lying. Minor hypocrisy can lead to major hypocrisy, thereby nullifying deeds. If lying is a grave sin, it requires repentance, and it is not expiated by acts of obedience that only expiate minor sins. It is not permissible to persist in lying under the pretext of expiation through remembrance of God (dhikr), for "there is no minor sin with persistence." Lying while performing acts that expiate sins is akin to secretly intending to commit a sin with the intention of repenting, and this is forbidden. The warning in the Hadith applies to those for whom these characteristics are dominant, not to those who commit them rarely.