You could try an extension tube for a 50mm (equiv) prime. Cheaper than a macro lens. If you have a tripod, you can ghetto use that as a copy stand and you can ghetto use an ithing (phone or pad) as a light box - just put a few coins under the slide to raise it off the screen as I got weird results. A dedicated lightpad is better (but more expensive).
If that's no good, I made this for mine (a while ago!)
Neg Scanner by
Ian, on Flickr
It worked as a proof of concept. 50mm lens (on an APSC camera) with a 20mm extension tube allowed the negative to be in perfect focus at the distance of a bog roll inner (which is also 52mm and sits perfectly inside the old Canon 50mm with a UV filter on it). Obviously folded paper won't do as a neg carrier, and I was going to try cutting slots in the bog roll to feed the negs through, but instead decided to just buy a flatbed. Might work better for slides as they're less flexible. Could just point it at a window and it really did give pretty good results. As I had the 50, the cost was a set of 2nd hand extension tubes off eBay. Having no clue what lenses you have, what their diameters are, what extenders are available to you, how close you can get with them, etc, etc, this may be no help at all. But it might be.
Good luck!
