Prazi and Panacure treat different parasites. For nemotodes, panacure would be the drug to go with.
For the question about can the average hobbyist do fecal exams- if you have a microscope you could. I'm sure you could get a used one that wasn't too expensive and find pictures on the internet or pick up a good fish medicine book to help you identify what you are looking at. You should be able to learn how to tell what a nemotode looks like. You could even learn to take a skin scrape of a ray that you think has a bacterial infection, look at it under the microscope and see if your sample contains an abundance of backteria. Might be very cost effective over the long run. It might seem uninteresting to many, but think of the stuff you could learn and how much more of an expert you'd become over time! You could also get used to necropsying dead fish and getting some idea of what killed your animals. Again, you'd learn so much. There is a bit of a learning curve but we all start somewhere. In the days before most public aquariums had vet staffs, aquarists did necropsy, looked at things under the microscope, plumbed our own systems, etc and were better aquarists for it.