OK it seems as though I will have to go into a little more detail as you don't seem to grasp what is going on. Firstly I agree £150 is not bad but not for a once a day service at random times throughout the week I think most people would imagine a low cost provider to be sub £100 especially bearing in mind the prices I am quoting are the base costs BEFORE baggage or seat allocation if you want it.
Then lets look at the next level of detail. My analysis is looking from the point at which there is only one provider i.e 11th August i.e 21days in August. If you look there then IOM to Gatwick there are four days when the lowest fare is £57.99 with most being around £100 one way and some as high as £153.99. Then lets look at the return leg Gatwick to IOM for the 21 days there is one day where the ticket price is £33.99 and thats when it leaves at the very unhelpful hour of 8.05am . The remaining dates again vary and can be as high as £163.99. Combine these together and you end up at return ticket price for most dates between £160.00 and £250.00 before luggage or seating. I don't think that's great sorry.
So sorry no I wont stop suggesting the ticket price for a one a day service from a low cost airline is high the facts are the facts!