Tours to Bulgaria in July experience the peak season. The air temperature is +27˚C, at night is rarely below +20˚C. At the same time, the heat rarely reaches +30˚C due to the light cool sea breeze. The water in the Black Sea warms up to +25˚C. All sea resorts of the country at this time are full of guests. If you want to avoid the hustle and bustle of Golden Sands or Sozopol, go to Aheloy or Akhtopol, there may be fewer people.
But to be honest, there are a lot of guests everywhere. Prices for vacations in Bulgaria in July are high, but it largely depends on what you expect from the trip. You can pick up inexpensive tours or cheap, and yet quite good quality accommodation.