Munich is more expensive. But Frankfurt's housing prices are rising dramatically recently. My wife and I are currently looking at houses (to buy, we currently rent one...) in the Taunus-mountains (about 10 kilometers away from the luxury homes I mentioned), because only there we can find large enough houses under 500k€ (which, even considering my 6-figure-income, is the maximum I feel comfortable with). Small 120sqm-row-houses, new, in Frankfurt now cost around 800k and everyone I know wonders who are the ones that can afford them and still sleep at night.