Suggest you contact Thai Embassy and check requirements there. Obviously at the moment no foreign people are being admitted to Thailand at all until further official notice.
Border is closed to non Thai people. No flights. It appears you have no idea of current situation. There is a pandemic.Before border was closed a requirement was that you had USD 150,000 of insurance cover of Covid Insurance.
Will be lucky if there are any scheduled flights to Athens by end July irrespective of price. Websites may offer prices but there is no guarantee planes will be flying. Very much a buyer beware situation until all the various authorities come to an agreement.