Commentary for Gittin 115:26

[Tosfot quotes the Gemara:] "for whatever [amount of] money that they demand." [He was legally allowed to do this because where] there is a threat to life, we redeem the captives for more than their value. [This is like what] we say in Chapter 'Hasholeach' (above, page 47a) about one who sells themselves and their children to idol-worshippers, [and this is true] a fortiori here where there is a murderer. Alternatively, [he was allowed to redeem the baby for more than its worth] because [it possessed] great wisdom.