I'd expect that at least one seat per flight was sold at the 'lowest' price, and after that they ramp up towards departure.
That is how Loco works, and if it appears misleading, (and I'll agree with you that it's not totally honest) then that's all part of the 'smoke and mirrors' required to fill the seats, mostly, we hope at an economic fare.
So what's a fair fare? At least 50 quid!
Lawyers? concur