Cost of living in Lille (France) is 41% cheaper than in Zurich (Switzerland)
This comparison has some inconsistent or sparse data. It already provides a reliable comparison but it is not bullet-proof. It is based on 1,018 prices entered by 176 different people.
For example, to keep the same standard of living that would require CHF 11,000 in Zurich you would need to make just about CHF 6,456 (€5,547) in Lille.