You're likely better off to just buy/make a high lvl heirloom set and do it yourself.
You're going to have to pay for their loss income, plus time, plus, plus, plus.
Not to mention they're going to have to leave their guild for 2 hours - which is going to involve permission from guild owners.
You're probably asking for a 10k fg session from someone to even make it worthwhile.
Maybe lvl 20 would be too ambitious but a few levels should be anywhere between 1-5 minutes per guild level which is quite incredible.
Definitely would have to make up for their income loss but that's not 100% of their income either. THey'd be losing xp for an hour or two plus the point of this is for them to make profit so there's that

.
I respect that heirloom item idea but even that would at best push me to maybe 10m xp per action whereas the top / medium xp battlers can make 200m+ per action.