It's very possible, especially if you keep an eye out on websites such as eBay, but at that price point one would have to wonder about a couple of things such as the bag's condition (if it's close to 50% off current retail then there's a very good chance it's priced down like that for a reason).
It won't be easy, but if it's a bag that you would really love and plan to have for years to come then don't settle just because of the price point. There's no chance of the Speedy being discontinued so take your time, save up a little here and there, and wait until the 'perfect' one comes along (whether it be gently pre-loved or new).
I've been admiring it for a long time and only decided to hunt it recently I set $700 for a preloved but will never go above that for a used one. Like you've said, i'll just save money here and there to get a new one