Go through your results for flights to San Luis Potosi in Mexico with Netflights. Although Lufthansa usually has the best prices, it's best to double check what's available for your travel dates.
If these flights are too expensive, try searching for a different time of year. So if your dates are flexible, consider looking at different times of year.
So, if the flights to San Luis Potosi don't work for you, you could always try searching for flights to other airports in Mexico.
You can also broaden your search by looking at more than one departure airport. Have a look around – you might be able to save by flying from a different airport or city.