My first answer was just to walk you through the math that you'd specifically asked for. We generally don't recommend this type of analysis, but we also recognize that it is done very often in practice, so we often find ourselves explaining how to do it.
If I were analyzing this project, I'd try to get stakeholder buy-in on running simulations to find this information instead. Simulations take competitive effects into account, adjust for product similarity, leverage individual information better, and are tunable. I much prefer finding out how price sensitive people are given a realistic scenario than I am finding out their price sensitivity in a vacuum.