Unpaid trial for a junior role. Take it or pass?

They offered a three-month unpaid 'trial with a view to hire.' They'd write a reference and I'd get a real project for my portfolio, which I want. But I need rent money, and I can't keep applying forever. How do people weigh experience against bills? I don't want to be taken advantage of, but I also don't have a huge runway. Would it change anything if they paid a small stipend?