1)    A person may not interrupt his prayer by speaking. It is even forbidden to signal with one’s fingers etc. If a child is crying and disturbing his concentration while praying one may signal with one’s hand to remind him to be quiet. If even this does not work, it is better that he should distance himself from the child who is disturbing him, rather than speaking. (Shulchan Aruch and Mishne Berurah 103)

2)    One may not interrupt in the middle of the Amidah even if by keeping this law it will cause him financial loss. (ibid)