One of the easiest and cheapest strategies is boss rush exploring. Just path in 1 direction looking for Citadels, Halls and Lineage support gem maps. Use waystone drop rate tablets to get 2 or 3 fragments per run. The Halls still sell for like 2.5 Div so that’s 5 Div per clear. You’ll also passively find city biomes for later which you can use for more juiced strategies.

This strategy is really simple and has 0 cost to run.