So I spent the last few weeks keeping track of my hacking results.
Average data site: 4m
Average relic site: 12m
NULL SEC / WH
Average data site: 12m
Average relic site: 35m
Level 3 and 4 sites definitely (but not always) pay better loot than level 1s and 2s. I did most of my null sec and wh hacking through wormholes, so there’s a good mix of factions. But Sansha sites definitely pay out the most (my highest was 102m from a level 2 Sansha relic site).
But assuming you’re roaming in null / wh space, and can find a relic every 20 minutes, you can make 100m per hour, and probably significantly more in Stain. Not too shabby.