kohtao.com Lotus Resort $14/nt best from SIN where you are.

Since you say "low cost" it helps us to know where you live (what airport you'll be flying out of). Airfare is almost always the single biggest expense of any trip. So choosing somewhere in your general part of the world can help keep costs down.

I'm on the west coast USA so going to Mexico or Hawaii are my two favorite places that are cheap, easy to get to, and very fun and active vacations.

I have stayed at many HI Hostels in the US and Canada. They have hostels in many other countries. http://www.hihostels.com/
Having a kitchen so that you can cook your own meals saves a lot of money vs. restaurants.
The Hostelling International hostels are generally better than Backpackers and the independent hostels.

Singapore is a great jumping off place for the rest of SE Asia.

When my husband and I were in Singapore, we took a side trip to Bali, which was really great. We spent a little over a week there, but could have easily spent 2 weeks. It is a short flight from SIN. We divided our time between Ubud (jungly, artsy town in the interior) and Amed (series of small villages on the northern coast).

We are considering another trip to Singapore and side trips that we are considering are: Thailand, Malaysia (Taman Negara plus some time on the coast), and Java (Jakarta plus Borodobur).

Oh then definitely stay in that part of the world. Your budget will stretch so much further that way. And there's plenty of wonderful choices (i've never been but friends love and return to thailand, indonesia, etc etc.)

Thailand and specifically Bangkok will certainly be a good choice, Spain is also a nice option ad if have to go for natural beauty then I would recommend Costa Rica or Tahiti.

i second Costa Rica. gorgeous!!!

I haven't been to Phuket, so I can't compare and contrast the two places, but Bali is amazing. There are the standard westernized beach resorts, but the island is very diverse. You have several different main beach areas, each with a different feeling. Amed is very remote and quiet, Kuta is party central, Sanur has a good tourist infrastructure but retains the village feel... Then there is the interior of the country - Ubud, other jungle areas, a really neat lake, etc. Because the major religion there is Hindu rather than Muslim, the culture is different from the rest of Indonesia. And the Balinese people seem to really put a high priority on art and craftmanship - it seems like every item is adorned beautifully, from panels on a wall seperating a family compound from the street to the gorgeous temples. We found this to be esspecially so in Ubud.