Hi Julie... I don't know that I really have an answer for you, but it's a great question! First off, the second generation antihistamines like Claritin and Zyrtec are going OTC partly because they are so safe to use and don't really require a physician't oversight in most cases. People like me who are uninsured like that they don't have to pay for a doctor's office visit in order to get relief for their allergies.
On the other hand, people who have pharmaceutical health insurance are unhappy that when drugs go OTC, their pharmacy plan no longer picks up the cost. Kind of a Catch-22 I guess.
As to why alternative, or natural, therapies are so expensive, my guess is because that's what the market will bear. Allergies are epidemic and medicines are expensive, so there is a huge demand for natural therapies. And when demand is high, prices will generally follow, unfortunately. Manufacturers of such remedies are rarely motivated by the "greater good" of wanting to see as many people as possible get healthier. They're motivated by the bottom line, almighty dollar, etc.
All I can recommend is that you shop around as much as possible. Different pharmacies and large box stores like Walmart may have vastly different pricing on medicines. Do look for identical generic versions; you can often save 50% or more by buying generic. For natural therapies, spend some time searching the Internet for the best deal. Again, prices can vary by vendor.
A quick search showed me that these salt inhalers generally cost under $50 and the salt crystals are said to last a long time. Since Claritin can be $10 to $15 for a 30-day supply, I think the salt inhaler actually sounds pretty reasonable... if it works. There certainly were lots of success stories at Amazon!
Hope this helps a little bit... Kathi