TK costs are based on your (pre-tax) income - but the German system assumes you'll be earning at least 1000 per month, so any less than that you'll still be paying 186.90 Euros. You also can't pay more than 816,75 - that's the upper bound no matter how much you earn. Some examples below:

Income: 1000 - TK cost: 186.90 Euros
Income: 1500 - TK cost: 270,00 Euros
Income: 2000 - TK cost: 360,00 Euros
Income: 3000 - TK cost: 540,00 Euros
Income: 4000 - TK cost: 720,00 Euros
Income: 5000 - TK cost: 816,75 Euros

Did this answer your question?