Go through your results for flights to Aachen in Germany with Netflights.
If these flights are too expensive, try searching for a different time of year. It's likely that prices for both flights and accommodation So if your dates are flexible, consider looking at different times of year.
Or broaden your search by looking at other airports in Germany.
For even more options, check what other airports you could fly to Aachen from. You might be able to make a saving by going from a different airport or city.