My advice is don't pay over £200 for one secondhand. In theory if it's from a dealer, it should come with a warranty of sorts...usually around 6 months (check what period it is for and up it if there's an option). Ultimately that is what you are paying the extra bit for. That is, peace of mind for that period...and that peace of mind costs you £50 by the sounds of it.
The wife has been very happy with her 300D. In fact I've never seen her take so many photographs!
Yes, I would agree this camera is soooooo slow...which pretty much rules out getting a good high shot selection if your into action or any high speed photography. Putting a high speed memory card doesn't make much of a difference either, as it's the camera's processor speed and short buffer that slows it up.
Check which film lenses you have and ask to try them on the 300D BEFORE you buy....to check they'll work (even ones listed as 'digi' compatible).
I don't blame you for sticking with Canon if you got the lenses AND they work.
Having said all this, if you're after a good secondhand Canon to get you into the digi world for general photography, and want a camera that can achieve some good high quality images when used correctly...this is an excellent start.
Much hinges on those lenses working (check no 'err' messages flash up on the LCD during or after you take a shot)... if the lenses, or just one doesn't work, way up the rpo's and cons of considering new gear.....
Don't totally rule out buying new.
DSLR's are continuing to drop in purchase price. High street prices start at less than £300 for Pentax's......a 350D body only is not much more than that coming in at less than £350, so too the Nikons....and they're quicker cameras
Hope this helps
good luck
cheers
Joe