This lot tend to be quite good (cheap!) - the Zante flight with them is on a Sunday though so would be the 5th.

http://www.olympicholidays.com/

As it's the school summer holidays you may not see prices fall that far.

As your talking about peak week holidays you're not going to get anything really cheap. Have a look at http://www.lastminute.com & http://www.alpharooms.com

You might want to keep an eye on First Choice's web site on the last minute part, its dead simple to use with lots of late deals.
We always use them for our hols and have never had a bad experience.
The prices get quite low sometimes its just a case of keep checking, bit pricy at the mo but will come down.
We always go away in the school hols and still get good deals!