My huz and I did this trip, and I think you could do it fairly cheaply...If you get good deals on airfare.
Land in Phnom Penh, Cambodia:
http://en.wikipedia.org/wiki/Phnom_Penh. If you haven't made travel arrangements beforehand, you shouldn't have a problem getting a place once you land. We took a taxi to the Foreign Correspondents Club, had a drink, organized a hotel. Cambodia has had a sad past (quick viewing of the
Killing Fields beforehand would give you a picture), but it is a vibrant place. And, if you don't stay at the crazily expensive Raffles Hotel (that would blow your budget), stop in the Elephant Bar,
http://phnompenh.raffles.com/z885/restaurants_05.html, for cocktails. Leave Phnom Penh for Siem Reap and the home of the spectacular Angkor Wat,
http://whc.unesco.org/en/list/668. You can now fly there from Phnom Penh or you can take the ferry/speedboat down the Tonle Sap River for a true experience and a lot less money. Be forewarned, if it's not the rainy season, you will be taking the speedboat. We did.
This does divert you a little from beach fun, but it's an amzing experience.
From Siem Reap, you can take a plane into Bangkok, Thailand. (There are probably other destinations but couldn't say offhand.) From Bangkok, you can take the overnight train to Surat Thani, and, then, take a bus to a ferry that will get you to Ko Samui. From there, we ferried out to Ko Pha Ngan,
http://wikitravel.org/en/Ko_Pha_Ngan, but you have many options from Bangkok. It was a beautiful trip. Great cultural attractions, learning experiences, and beaches!
That being said, Indonesia is supposed to be fantastic, and the language is, supposedly, very easy to pick up.