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What about making these modifiers, as in, during setup they're put on supply piles and do their thing. e.g.:
Mining...Cost: +1
Cards in the supply pile this is attached to get the text "You may trash this card immediately. If you do, +$2" after all of their on play effects.
Farming...Cost: +1
Cards in the supply pile this is attached to get the text "Reveal cards from the top of your deck until you reveal an action or Treasure. Put that card into your hand and discard the others." in place of the first instance when the card would draw or reveal a card from the top of your deck.
Border...Cost: +3
Cards in the supply pile this is attached to get the text "When you buy this, gain a card costing less than it."
Worker's...Cost: +1
Cards in the supply pile this is attached to get the text "+1 buy" after all of their on play effects.
Wandering...Cost: +1
Cards in the supply pile this is attached to get the text "Reveal the top 3 cards of your deck, put the Actions back on top in any order, and discard the others." after all of their on play effects.
Yeah wording could probably be better, but it's the bad card threads so whatever.