I picked up a digital zoom microscope that is supposed to be 500x for $15 the description is
S02 Portable 1X-500X Continuous Zoom 2.0MP Digital USB Microscope Black
SKU: 23003452
If you google the sku you can find several vendors. I happened to find one that had it down to $15.
The stand that it came with is worthless. It took some time to get anything in focus. I also did not have a decent way to hold the gem, so there are several challenges to overcome to make this practical, BUT this is the first image I was able to capture:

I think that it is worth working on a better stand that will let me control the focus and then probably some stacking software.
AT least for less than $30 I now can see the inclusions. ($15 for the camera, and $15 for some bits to make a better focusing stand, (I might be able to modify the one I made for my 35mm camera, but still need something to hold the gemstone,,,,, ) and back field illumination. BUT it is a starting point for very little money.

