For a low-cost DIY option, you could look at 3D printing a slide scanner. Perhaps your local library offers 3D printing services at a low cost? I work at a library, and my job portfolio oversees the "Makerspace" elements of our services, which includes 3D printing. I've printed a negative scanner in the past the worked by placing the mount on top of an iPad with the screen on at max brightness, displaying a pure white background. The "scan" would then be captured via camera/macro lens. 3D print design databases such as Thingiverse have many user-created design of varying utility and quality, but it could be worth considering. This approach surely wouldn't alleviate the tedium of the process, but could make it more cost-effective, at least.
Alternatively, your library may offer public access to flatbed scanning. My library has flatbed scanners with film and negative guides, the scanning utility, and then Adobe Creative Cloud for Photoshop, all available at no cost to members.
