Ticket class price difference

Just tipped my flying club miles over 65k so thought I'd have a look at possible ways of spending them.
On the VS site when I try and price up say a LGW-MCO Econony flight it always comes back as a Q class ticket, but this isn't one that can be upgraded with miles to PE.
The flight is currently coming in at £621 in Q so how much price difference would there be to get one in an upgradable ticket class to PE which I use miles on?
Makes sense? Its not urgent as just trying to get a feeling for the price difference in ticket classes.
On the VS site when I try and price up say a LGW-MCO Econony flight it always comes back as a Q class ticket, but this isn't one that can be upgraded with miles to PE.
The flight is currently coming in at £621 in Q so how much price difference would there be to get one in an upgradable ticket class to PE which I use miles on?
Makes sense? Its not urgent as just trying to get a feeling for the price difference in ticket classes.