To be honest, I would say go for a new XS or XSi (1000D and 450D). The "professional" models are pretty much the same, but the shutter will have more "actuations" (opening and closing...). There may be a few extra features on a "professional" model, but you'll probably not need them if your just shooting pens, artwork, etc. Buying used, you don't know how many pictures have already been taken. Yes, a camera might take 100,000 pictures before the shutter wears out and it may take 200,000. But they are all rated with an average life span, which is measured in actuations and unless you're a pro that's out there shooting 500 pics a day, the camera should last you many years to come.
Also, is there any reason you are looking at Canons? Nikon, Olympus, Sony, etc. all have great SLRs nowadays and you might find a better deal on a different brand. Don't get me wrong, my wife has a Canon and we both love it, but there are lots more "fish in the sea" you may want to consider.
And when you're photographing artwork, will this be for making reprints? If so, you'll want to look into some good lighting and nice tripod as well... (even for shooting your pens as well) and depending on how large your prints will be, you may want more than 10MP.