I use Corel's Paint Shop Pro. Lots cheaper than Photoshop, but almost as powerful. Definitely more powerful than Photoshop Elements for same price. GIMP is a fairly good shareware program, but is a bit harder to use than most. Skimpy online help, but there is a book published on using it.
I find using the Micro Mark set a lot of work. I am working on alternate ways to do homemade PE. I have used toner transfer paper (the toner acts as resist), and latest effort is using Cricut machine. So far with either, I cannot get as high a resolution as with the MM kit, but they are both useful for larger or less detailed parts.