Rob, you should be able to get a good 20D for around $600 second hand if you're wanting to test the water without spending a lot of money. 8.2mp is not to be sneezed at and will produce a fantastic image. The 20D can then be modded at a later date if you feel the need. It's worth noting that the 20/30/40D series is quite a bit heavier than the plastic fantastic 350/400/450D models. The shutter is also more robust in the 20/30/40D range.
If you're after a good starter lens at half the cost of the L series lenses, then the Sigma 17-70 F2.8-4.5 is a very good choice.
FWIW there's a 20D for sale in the
Icetrade section here.