Aviation is not low cost. The ability to get on a flight for a tenner is, to me, a crazy notion. That's why Ezy, FR etc, only offer the first few seats at the lowest price. From then on, the price will go up, by how much is dictated by demand and milking the yield. If you look to book a week or so before during the English half term, don't be surprised to spend £200+!! I think a return flight to England or Scotland for less than £100 is a bargain.
Often at late notice, switching to the more legacy type carriers will get you a better fare, especially when you factor in bags etc.