The power supply is the likely candidate as you have identified. It is not complicated to replace it yourself. First step is to identify the specifications of the original, and ensure that you are replacing with like for like (or higher capacity).
Then, you can find how to guides on Youtube like this one...
http://www.youtube.com/watch?v=UzolRkN7Eew
'How to Replace Your PC's Power Supply'
So if you feel up to that you can save yourself a lot of money. If I were you I'd mark with stickers all the plugs and sockets on the old PS and connected components, or make some kind of sketch of them so you have a cue to help to remember what to plug into which from the new one.
p.s. By the way I'd expect to pay from about S$50 for a decent PS...