Answer that you'd pay up, but secretly plan to refuse. This means you'd be lying to us here in the comments - surely not a very nice thing to do. But if you subscribe to CDT with respect to utterances as well as actions, this is the alternative you're forced to choose. (Which may or may not make you uneasy about CDT.)

What makes me uneasy is the assumption I wouldn't want to pay $100 to somebody who rescued me from the desert. Given that, lying to people whom I don't really know should be a piece of cake!