Fines in Germany usually follow the "Tagessatz", which is the income of a day, as calculated based on your tax records (and other information). So you might be sentenced to pay 90 'daily incomes', which hits a poor person as badly as it does hit a rich person.

Also note that there is a minimum amount of income that you always will be granted access to ('Pfändungsfreigrenze'), so a fine will not make you die from hunger nor make you homeless.