An undergraduate said they may hire a freelancer to do their work for them. What should I do?
[The student] remarked (in writing) that they might as well just buy solutions to their projects on a particular freelancing website for that price, as their friends do.


That does not sound to me like "admitting" that they "would" cheat. If I said to a prospective financial advisor, "your rates are so high I may as well just declare bankruptcy now", that does not mean that I am going to declare bankruptcy, it is merely a way to express that the advisor's services do not seem cost-effective.

Given this, I would do nothing -- you offered legitimate tutoring services and the student declined your offer. You have no compelling reason to suspect that the student will actually cheat.