Thailand is indeed very cheap. Koh Pee Pee is stunning. I was there pre - tsunami and absolutely loved it.not as touristy as koh samui and very romantic for a couple.lots to do there.beautiful beaches and great nightlife also. great place for activities like cliff jumping, scuba diving, boat trips, etc.
koh samui is also beautiful...a little bit more commercial though but stunning also.
have u considered splitting the holiday in half? as in doing one half up north and the other half on an island... the north offers great treks in Chang mai where u stay in the rainforest for a few nights and go trekking, bamboo rafting, elephant riding, but maybe u do not fancy this for your honeymoon?
Thailand is very cheap and a beer will cost you about 40 baht ( 1 euro approx) on average
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