I have a canon 400D (I believe the same range as the rebel) which cost me £300 ($600) body only, it's a consumer/amature level camera, $2000 will get you the canon 5D which is a full frame camera (unlike the 400D which is has a crop factor of 1.6). All digital SLRs have a manual setting, $2000 isn't required for that, even most compacts have the ability to manually adjust the F number and shutter speeds.
I highly recommend the 4xxD or the Nikon D40, both are great cameras for the casual SLR photographer.
If we're talking about digital SLRs, the aperture is soley dependant upon the lens, the lens you will either get with your camera, or you can buy some. Like film SLRs, you will have a whole range of sizes to chose from. From wide angle, where you'll get a wider field of view, to Telephoto, where things are zoomed in. Of course zoom lenses are a lot more conveniant and I very much recommend the sigma 18-200mm, as this will cover pretty much all you'll need. As far as shutter speeds is concerned, most current digital SLRs have a shutter of around 1/4000, you don't really need to worry about it.
Comparing digital to film; I'll talk through the main differences.
Firstly in the consumer and pro/sumer levels the sensor size is smaller than 35mm, the main affect this has is that you'll find that your wide angle lens wont be as wide angle, lets say you have a 15mm lens, on a digital camera with a crop factor of 1.6 it will become the equivilant of a 24mm lens. This does mean a reduced image quality due to the effects of noise and chromatic abration (cyan and magenta fringing around the edges).
Also you can change the ISO frequency on the go, unlike film cameras where you need to change the film if you wanted a higher/lower ISO.
Obviously your pictures are stored on a digital medium instead of as film, this means you can store a greater volume of images on a single card than you can on a roll of film, also you don't have to worry about dust and scratches affecting the original photographs.
As far as the quality goes, if you're looking to print A4 sized images, there isn't much difference between film and digital, especially not 35mm.
Hope I've helped, feel free to PM/get in contact with me if you have any questions.
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