Basically you use a lightbox, as in what is used to view slides and transparencies, to backlight your slide. Create a cardboard cutout 'template', so your slides will be in the same position each time on the lightbox [also good to 'black' out the rest of the lightbox, so no light leakage (thereby affecting your exposure settings). Then set-up your camera on a tripod and zoom in (optical only) and focus on the image within the slide frame and use your remote/or timer to photograph the slide. Further reference here- http://www.pbase.com/lowthian/digitizing_old_slides
As for the CoolScan, they often pop-up second hand, usually by people in the same position as yourself, ie- needed to scan x amount of slides, then pass onto the next person.