[baro-nite]

We would want a magnification range of 1X to 20X

Does this mean the final output needs to be up to 20x life size? Or are you trying to achieve 20x at the sensor? The latter is the more usual way of describing magnification in macro photography, and is what most of the answers above assume. There's a huge difference: the former can be done well enough with an ordinary DSLR and macro lens; the latter requires microscope optics to get meaningful detail at that magnification.