It's very hard to find hillside land with 180 degree uninterrupted sea views, but here's a very nice 2 Rai plot. Ideal for a house or two. And the good news is that is it one of the cheapest plots on the island - only 2,000,000 Baht/Rai with a Chanote title. See for yourself here
Also worth a look is a discounted housing plot on the luxury Siam Royal View development, only 40m from the beach and the only remaining plot end plot. Big savings on the developers listed price.
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Not a lot of new listings on this site recently as although there are a lot of businesses and small resorts for sale on Koh Chang at the moment, the vast majority of owners are asking very high prices and can't back that up with annual profits that would make the investment a worthwhile one.