Welcome to the CiC Forum...
I cannot give you an idea of prices since I live on the other side of the Atlantic from you but, I am very familiar with virtually all varieties of the Canon 1.6x crop cameras which is what you should be aiming at.
I shoot with cameras from the D60 which was the second Canon DSLR camera in the 1.6x format (after the D30) to the latest 7D camera. Any of the Canon DSLR cameras will provide good imagery however, I would recommend that you go no older than to Canon 20D or the Canon 350D (AKA the Canon XT).
The Canon D30, D60 (not to be confused with the more recent 60D) and the Canon 10D are limited as to which Canon lenses they can accept. They cannot accept the AFs lenses so you are limited in lens selection. This eliminates the capability to use the 18-55mm f/3.5-5.6 IS lens which is a decent lens that sells for a very low price Note: The IS designation reflects Image Stabilization which is Canon's name for their shake control system. I also would not get the Canon 300D (AKA: original Digital Rebel) because this camera is limited in certain respects.
I had a Canon 350D which, although certainly not the most capable camera in the Canon lineup can deliver quite decent imagery and is pretty versatile. The 350D along with the Canon 20D should be the least expensive cameras on the used marketthat I would consider. There should be a lot of them available however, they will often be paired with the original 18-55mm f/3.5-5.6 lens which does not have Image Stabilization and which does not produce quite the image quality of the IS lens. The problem with this generation of cameras is that they have been around for quite a while. This would be of no consequence if they were kept in a drawer between birthdays and vacations but, might be a problem if they were given hard use.
I would not limit myself regarding pixel count. I shot with a Canon 10D which is a 6MP model for years and it did very well. Until recently, I shot with an 8-megapixel Canon 30D along with a 10-megapixel Canon 40D. BTW: I still use the 40D on a daily basis along with my 7D as a two camera combination. IMO the 40D is probably the very best value in the Canon used line if you consider price against capability. But, it might be a bit above your entry price. My photos from these two cameras are available at (
http://rpcrowe.smugmug.com/ ). All the images in my China galleries were shot with either the 30D or 40D.
Here are two examples:
I am wondering if, for your budget, you might be better served by considering a Bridge Camera such as the Canon G12 or SX40 or a Nikon or other brand equivalent I am not really familiar with these cameras but, they are more in your price range and come equipped with a lens for under 300 quid on your side of the pond. Perhaps someone more familiar with bridge cameras may recommend or not recommend their purchase...