The issue is that the price of gaining /xp/ rises dramatically, so a higher level brewer is paradoxically paying a much higher price to brew than a presumably less skilled one. So just reduce xp cost as your level goes up, because 500 xp at L6 is worth a lot less than 500xp at L10. By how much is the real question... You could compare times to earn it in average quest durations by levels... By no means perfect since it doesn't take risk and resulting xp loss into account.