Roy and Carol are an elderly couple living in a Sydney suburb. Roy has been suffering from a respiratory disease and Carols mobility is very limited. Roy does all the shopping for the family but during the pandemic, he was fearful due to his extreme vulnerability given his age and condition. Roy approached Nathan, whom he knew personally, to ask whether he could do the shopping for the couple once a week. Nathan agreed but said that he would charge them $200 per hour for the task of shopping. Roy knew that the hourly rate proposed by Nathan was unreasonably high but agreed to it without having an alternative. With the pandemic fears now reduced, Roy remains thankful to Nathan. However, he is very upset about the hourly rate charged by him.

Required:

Advise Roy if he can challenge the validity of the contract with Nathan on any ground under the law of contract. Please refer to case laws in support of your answer.