CN = cloudynights. But be aware there's shipping costs from the US so you need to evaluate if its worth it buying from overseas or getting locally, or even buying new. Case in point: Antares Plossl: $40 locally. Selling maybe 20-ish on US market. Plus shipping, more than cost of new item!
Anyway, this ad might interest you
http://www.cloudynights.com/classifieds ... st7&page=3
Its a celestron Ultima 2x Barlow, I'm under the impression its a good piece. Asking USD 50 inc US shipping (est $5), you can ask to top up $5-$10 for Int'l shipping (First class mail at 1lb is about 10-ish). Top end, assuming no bargaining is USD60, or SGD 80 or so.
3x barlows are very "powerful". If you think about the average scope, say an f/8 system, the widest EP you can usefully use will be 7x8=56mm ( as it will give an exit pupil of 7mm - you can use wider but it will produce a visually darker picture) A 3x barlow on that will be 18mm, which is a large jump. Intermediate range EPs such as a 17mm will now become a 5mm with 3x Barlow. It might be easier to plan your focal lengths with a 2x as the jumps are not that severe.
Having said that, if the magnification does not exceed your telescope's limits or seeing conditions, a good Barlow should just act as a magnifier: i.e. perform the same as an EP of similar focal length.
As usual not being very experienced with telescope optics yet I'm extrapolating from my knowledge of camera lenses, so if anything in here is wrong, please feel free to correct me
"The universe is composed mainly of hydrogen and ignorance." 
