In July and August the biggest savings come from moving one step away from the famous name: Split instead of Dubrovnik, Chania instead of Santorini, Thessaloniki instead of Athens. Book accommodation early, as monthly rates in coastal towns rise sharply after May, and look at June or September if your dates are flexible. Prices are often a third lower and the sea is still warm.
Fly midweek and avoid Saturdays, when most package holidays travel. Summer is also peak season for delays and cancellations, so keep your boarding passes: under EU rules you may be owed compensation, and Compensair can handle the paperwork.
On the coast, the best beaches are rarely the ones next to town. A small car for a weekend often costs less than two guided trips; Localrent lists local rental agencies with simple deposits, and on the islands a scooter from BikesBooking is usually enough. If you're crossing borders, one eSIM like Yesim saves buying a new SIM in every country.