I'm thinking of rejecting his proposal because I'm not ready to marry unless for money.
I feel like you got the wrong idea for marriage. Why are you only going to marry because of money?
I'm not fully convinced.
It sounds like being married is not something you're ready for, and that is okay. You should probably talk to him about your doubts before he proposes.
It's fine, I'll reject him.
You will hurt his feelings if he proposes to you publicly, so I do suggest that you communicate with him privately that you will be rejecting his proposal. I still think that it is wrong of you to think that you can only marry someone because of money and just consider that you should marry because you love the person, and not for their money.