Costs for tiler - 203 sqm - 28k euros gross - Is the price reasonable?

Calibrated tiles usually go hand in hand with the desire for very narrow joints. Installation is more complex because slight overlaps are more likely to occur. You basically can't avoid using a leveling system anymore if you want to stay within the standard.

The offer is convincingly detailed and not too expensive. You can get it cheaper - certainly. If the provider works cleanly and reliably, that is fair. A good craftsman must not and should not be the one with the lowest offer price. In case of doubt, it is better to save on building materials than on the craftsman's service. Unfortunately, the latter is difficult to assess in advance. If necessary, look at references.