Taking a vacation!!! Any suggestions?

Hi all, I'm working in Singapore as a teacher, which means I get a few vacations sprinkled in throughout my year.  I have one coming up in September, and I'm wanting to take off for a week with a budget of (about) S$700.  Where should I go?  I'm going to Malaysia in October, and I've already been to Thailand and would like to try something new.  I'm thinking Bali, but am open to suggestions.  Also, if anyone has any tips/advice for 1)traveling solo- which I don't mind doing but seems to be more expensive with no one to share costs with, or 2)any tour groups or how to get in contact with people to travel with so I don't have to go everything alone.  I have friends here, but they don't have the vacation time I have. 
My traveling style is really laid back, frills are nice but not necessary.  I'm in my young 30's, female, active, and would enjoy being constantly busy during my holiday just as much as I would enjoy sitting on a beach for a week.  I've traveled a lot on my own, but it's always nice to have company, so again if anyone has had a good experience with a group or any suggestions, I'd love to hear them!