While I disagree with most of the proposals (either the pay or the outcome or both), they are akin to being paid for contract work. Would you tell a contractor what they can do with the money they are paid?

It would be like hiring a painter to paint your house, then telling them they can only buy pink Barbies with their money.

Once the money is theirs, they are free to use as they please provided they satisfy the requirements of the proposal. If they want to put it in savings or spend it on a lifetime supply of bananas, that's their right, something you have no say in.