When considering expansions, some of the cross-set card interactions are covered here...
With just that set alone, Lifebound Initiate combos with Snapdragon (5/2 l/c... 5 cost, 2 honor; lifebound construct) which says you get +1 honor for the first l/h you play. This card also pairs with Runic Lycanthrope to get +2 power as well. Void Initiate is nice early on to thin out your deck of Militias and Apprentices.
It may be a good idea to buy these as a cheap way to get new cards into the CR (center row). In your OP, you mentioned higher cost cards, but also Monsters. If you have 1 rune and 8 power, buying one of those cards could clear the way for a juicy Monster for all that power to kill.
Cross expansion stuff not covered in that link...
Immortal Heroes (exp #3) -has an Enlightened event where each Enlightened card you buy lets you draw one card
-has a Void event where each Void card you get lets you banish a card from your hand or discard pile
-There are cards that look for # of lifebound cards played, or have Unite effects, or Multi-Unite with Realms Unraveled (exp #6)