Cost of living in Liege (Belgium) is 16% more expensive than in Zaragoza (Spain)
This comparison is lacking data. It provides a decent comparison, but it is not yet reliable. It is based on 239 prices entered by 18 different people.
For example, you would need at least €2,081 in Liege to maintain the same standard of living that you can have with €1,800 in Zaragoza.