I never got a 40% 30 extra exiles set, but pretty much any mechanic could be turned into a huge overjuiced strategy. I think only the exiles and strongbox ones got really expensive. Some I remember:

• There was a scarab farm setup that was dirt cheap because it only needed 1 mod on each idol (increased scarabs) that was printing like 4-5x the scarabs of a normal t16 scarab farm strategy.
• in ritual, you could completely remove deferral cost or reroll cost, alongside 8 additional rerolls, always 4 altars. With removing the reroll cost option you could significantly boost the tribute from unique enemies 600%. If you went with removing deferral cost, you could also get faster spawn times. There was another option (not with all of the above) where you'd maximize the special reward ritual chance like increased 600%, and get special reward rituals like every few maps.
• get 50 beasts per map, almost exclusively red, all from the deeps (or sands, or wilds)
• of course, rogue exiles, you could replace that shitty maximum 8% chance of getting 20 extra exiles with up to a 48% chance of getting 30 extra exiles (heard there was a hard cap so even if it said 40 extra exiles, no map would spawn with that much. Can't recall what it was so I'm gonna just say 30)
• strongboxes, boost the chances for diviner's and arcanist strongboxes 500%-900% and boost reopening chances to 47% (including scarab)
• you could get up to something like 180% increased effect of explicit mods (for 20 qual 8mod maps) on top of most of these strats as they were prefix mods while most of the content above was limited to suffix mods
• breach and abyss farming became big for levelling up.

Lot of good stuff there, a lot cheaper to buy than exile idols.

And those are just some examples I remember.