I agree that the cost can seem relatively expensive if you haven't done a lot of salmon fishing before, but the Miramichi is a bargain compared to to some salmon lodges that can bill $20k a week.
When fishing a new river for the first couple of times, a guide can be worth their weight in gold. Local knowledge of the water, where the fish are, and how to fish to them can make the difference between a solid skunking and having a great trip.
Rural NB does need the employment provided by guiding. One might think of it this way - the Miramichi is local NB treasure. One way to leverage that resource and generate local revenue is to require those visiting from out of province, taking advantage of the bounty of the river, to pump a few $ into the local economies.
If you're really set on very economical salmon fishing, most rivers in Quebec have unreserved public sectors for very reasonable rates ($40-$75 daily). However, my point about using a guide for figuring out the waters, knowing where the fish are, and how to fish to them instead of floundering around on your own still applies.
The costs of fishing the Miramichi seems exorbitantly expensive. My girlfriend and I will be driving from the east coast to Ottawa in June and wanted to stop to fish the Miramichi for a day. Once you add a modest night's accommodations ($80), the cost of a day's guiding ($250-300), and two 3-day fishing licenses ($130), you're paying over $500 for a single day of fishing. As young adults/students it becomes unfeasibly. It's too bad they've made the river financially inaccessible to some.