I am an American expat with a retirement via living in Thailand. I would like to live three months out of the year (April, May and June) in a different country. My criteria for this country are as follows: must have pleasant temperatures during these months in the 70's F (25C); it must have 90 day visas on arrival or available for purchase; cost of living must be comparable to Thailand or cheaper; flight duration no more than 6-7 hours one way. Any suggestion? Thanks in advance.

There are a number of EU Mediterranean countries that are nice... Spain, Southern Italy or Greece

 

American get 90 day stay on arrival

I would recommend Cyprus ... pleasant weather, English speaking lovely people, great facilities, as cheap as Thailand (cheaper for a long termer), not sure about flight time but it is on the edge of Europe that is closest to Thailand. 

Flight time's a bit longer, but Morocco is fascinating and not expensive.

 

Someplace like Guangzhou in S China is relatively near and not expensive; 60 days per stay on a 10-year visa, but easy to reset with a visit to Hong Kong or Macau.