I've done this with the clear deli containers. I do like that they tend to be more sturdy than many other plastics. On the downside, I don't get many of such containers as I very rarely buy such premade foods.
A cutting wheel on a Dremel works well for slitting pots as well and a drill can be used with stiffer plastics for holes.
If you do use the melting method, then do be sure to do so in a well ventilated area. The fumes/smoke from the plastic is not something you want to be inhaling.