The fixtures
El Clásico, Madrid and Spain's local derbies
Real Madrid against Barcelona is the global headline, while Real Madrid against Atlético brings the rivalry into one city. The Seville derby between Sevilla and Real Betis, the Basque derby between Athletic Club and Real Sociedad, and Barcelona's meeting with Espanyol each have their own local edge. These games tend to have less flexible inventory than an ordinary league weekend.
Club form matters, but timing matters too. A match late in the season can become a title, European-qualification or relegation decider after tickets first appear. Compare the options available while the stakes are still uncertain rather than relying on a generic seasonal average price.