I have been using wet/dry sandpaper on a marble tile for lapping my stones. It has worked quite well, but the paper tends to move around and it curls over time. I have used a few different types of sandpaper, and have found that the wet/dry sandpaper from Harbor Freight works well, it has a tendency to have sections of the abrasive come up, but it has a slurrying action, so it's ok.
Anyhow, I used my Chinese Natural to polish another stone, and a chunk of the CNat came lose and scratched the heck out of one corner. This had been ok since I was able to use the rest of the stone. A few weeks ago, I thought it would be a good idea to use some slate slurry on the CNat to see if it would act more quickly, well, it destroyed the nice surface finis it had, and though it still provided a good edge, it was nowhere near what it had been. This meant that I had to re-lap that beast of a stone... I knew that it would be quickest to use the 220 wet/dry, and had come up with an idea for a setup that might shave some time off the lapping. First, I used a 6" wide piece instead of the normal 3". Then I used a new technique for attaching the sandpaper to the marble. Binder clips!
The picture above is of the setup after lapping out the scratches out on the first side. It took all of 12 minutes! The slurry it created was so thick and muddy, I couldn't believe it! I was adding a good amount of water every minute and a half. I then decided to tackle the second side, the side with deep saw grooves (which is the side you see). I had worked a lot on the second side before, but never got things worked out, but I thought this was my big chance as long as things were set up anyhow.
This is after 3 minutes! Thick pasty slurry! I doubt you can see the difference in the saw marks between the first and second, but with another 15 or so minutes of rubbing, they were all but gone (some remain on the very bottom edge of the stone). I also chamfered the edges as long as I was at it. After I had pretty well taken care of the 220 grit paper (almost no abrasive left in the middle), I moved up to 500 and then 1200 grit.
If you want to get a great lapping setup for under $10, give this one a try!