Making Money in a low-tech setting

[Vent0]

Forces and Matter for Blacksmithing.

Or Time, Forces, or possibly Death for food preservation. Maybe even Matter (vermin can't eat your precious grain if it is in an air-tight, vacuum stone vault).

[Neos01]

And mind magic allows to boost professional skills, read useful secrets, convince people to lend money...

[lnodiv]

A mastigos could use space magic to bypass all the risk of a long journey, so he could be an excellent merchant

Or courier. Getting messages from place to place in a lower tech and/or dangerous setting can be a very big deal.

[Neos01]

A mastigos could use space magic to bypass all the risk of a long journey, so he could be an excellent merchant