We have cut thousands of ABS cases, but in general, it's difficult to align materials well in the laser cutter. The cuts are very accurate relative to each other, but the material is just placed on the table and therefore just aligned by eye. Typical accuracy might be +- 1/32", which is quite a bit if you want some other parts like LEDs or switches to line up well with the cutouts. Whether or not such results would be acceptable will depend on your application. For those customers we have cut cases for, there is an initial setup charge for making a jig (maybe around $100, depending on your cases), and then unit costs around $1 when we do several hundred cases.
Another option is to use cases that have 1/16" inserts for the end panels. We can then cut a whole new end panel out of a new sheet of plastic, making the cutouts much better registered to the edges.
So, ultimately, it depends on your case, how much you want it to cost, and how accurate you need the cut positioning to be. If you would like to pursue this further, we would need to see the case and what kind of cutting you want done.