I keep a watch on ebay for bargain Canon 450Ds and that's how I found my current spare for less than $200. There is a local (au) one sitting there now for $180, which if the ad can be believed was only ever a backup camera so may have little shutter count:
http://www.ebay.com.au/itm/Canon-EOS...item4af0e758f7
There is a local (au) 1100D up in ebay au as well (bids required) from $150 that would be worth watching.
http://www.ebay.com.au/itm/Canon-EOS...item3ab21fc0e5
Plenty of them around the world (US and UK especially at reasonable prices if you don't mind the shipping, but local buys are usually more cost effective. Even supposed non-working cameras can be a great find, things like the shutter module are easily changed if your stripping it down to mod it anyway. You can buy new OEM shutter modules for about $50, and that's the only real wear and tear item you'd be worried about.