The Rosco LitePad looks interesting. A 3"x3" version is about $50. The main thing will be if you get enough light. With a continuous light exposure, we probably want to avoid shutter speeds from about 1/15th of a second down to a second, as these are the most susceptible to vibration.
Near the beginning of the main thread, I showed a stepwedge photographed with a dslr+macro lens made with one exposure, and one with blended exposures. There are certainly gains to be had there, if needed. While most bw negatives would fit within the dynamic range of one exposure, I just scanned a tech pan negative with no problems, digital images are noisiest in the shadows, and with bw negatives this means that the noisiest areas will be the highlights when the image is inverted. As a result, some type of multi-exposure blending could be very useful, especially in images with lots of very delicate highlights.