Does his price go up depending on the instance he is boosting you thru? if its just a flat 20g per run then I would maximize the instances that can give me the best xp gain per your level. So basically leave SM when the xp starts to go stale and you need more than 1-2 runs to get a level.
Go to ZF if he is a druid, or move to something like ST. If you plan it correctly you can maximize 30-50 with 23-25 (+- a couple) runs at 20g a run so spending less than 500g getting 20 levels with RAF.
It's that or level your pally to 70 and get the cobalt starter set and continuing your own boosting. Is the time spent worth the gold you would be saving or is the gold spent worth the time you will be saving yourself?