You can't have it all unfortunately. I've been visiting the western isles for 30 years as my father is from there. A nice place, with very nice people who are very quick to boast about how great a place it is and how wonderful it is living on an island. Unfortunately there are pros and cons no matter where you choose to live, and expensive flights are just part of living on an island.
Just like social media campaigns a few years back to protest about high petrol costs it is a fact of life that supplying products to the islands are high and that must be passed on to those who consume these products and that includes the flying up there.
You're never going to get a £19.99 all in flight up there. The closest was BMI Regional once time when I paid £56 return and that route lasted five minutes.
A lot of the times people are complaining about the cost of last minute fares which are traditionally higher anyway. That's the same for any airline. If I wanted a Ryanair flight tomorrow I'd probably pay a fortune.