I say, and with God's success: It is permissible, if it is based on the report of a just Muslim doctor, and it is not a condition to fear loss; because it is permissible for him to perform tayammum if water is sold at an exorbitant price, and the harm of the severity of the illness is greater than the harm of the increased price, thus tayammum is permissible for this reason; as Allah, the Exalted, said: {And if you are ill or on a journey or one of you comes from the place of relieving himself or you have contacted women and do not find water, then seek clean earth and wipe over your faces and hands.} Surah An-Nisa: 43. Refer to: Sharh Al-Wiqayah p. 105, Fath Bab Al-Inayah 1: 110, and Al-Tabyin 1: 235, and Allah knows best.