Make prayer potions. Items needed:
Vial of water
Clean ranarr
Snape grass
Clean the herb if it's grimy (grimy may be more or less expensive than clean), use the herb on the vial of water, and then add the secondary.
These give 87.5 experience each. It will take 1,066 Prayer potions to get level 52 from 38.
Assuming you buy all of the items on the Grand Exchange and clean herbs are used, you will spend (-) or earn (+):