If there's a few bids already, my guess is that it's a pretty good deal. 350D's still a good camera, but getting a 400D would be a lot more worth it because the 450D's just out. If you wait for maybe a while more, the new 400D's price will drop to maybe S$800.
The cost of a 200mm range depends on a lot of factors. Image quality (55-250mm IS versus 70-200mm L series), max aperture (55-250mm IS f/5.6 vs 70-200mm f/2.8L series), weight (again, 55-250mm plastic-built vs 70-200mm f/2.8L series @ 1.4kg).
Minimum cost for a new lens at that range would be S$360 for a new EF-S 55-250mm f/4-5.6 IS. It's built is plastic, image quality isn't exactly very superb, has image stabilisation, and cannot be mounted on film / full-frame cameras. Get this if you only have S$400 to spend.
Next up would be the 100-300mm f/4.5-5.6 IS USM lens for S$570 new. A lot better (in terms of image quality & built & ability to mount on your 35mm film / fullframe cameras) than the above, but has technical flaws such as zoom creep (when lens points down, the entire lens will extend like when zooming. For the price, there probably isn't anything quite like it in the range (of 300mm).
Right, next up would be the cheapest of all L (for luxury) lenses: the 70-200mm f/4L USM @ S$1000 new, S$800 for 2nd-hand. Superb image quality, metal built, and constant aperture. It's a lovely piece of lens, but maybe at 200mm you'd like some image stabilisation, I dunno. You can't go wrong with this, just that you'd probably have to stretch your budget a bit (but we don't know your budget, so yeahh).
You can't go wrong with the 70-200mm as it's the best series of Canon's zoom lenses, but if you can't afford it and aren't so nit-picky about image quality and stuff, the other 2 will do. Remember: you get what you pay for.
Hope this helps =)
