some personal observations:
(a) early prices on low cost tend to be lower than premium airline economy.
(b) late prices on low cost can be far more expensive than premium. [I've seen Easy at over £400 for a London Geneva return.
]
(c) low cost can mean
less restrictions than premium (e.g. Ryan & Easy flight times are changeable, with some differential cost attached. 'Premium' usually means throw your ticket in the bin. In fact, throw both legs in the bin, because if you don't fly your outward, you will be refused travel for the return
)