I'd be shocked if FFG prints Lucre but doesn't let you buy from the reward deck. I suspect it will be moderately more costly than buying regular cards.
What I'm getting at is Lucre gives an excellent opportunity to expand the reward deck. Just promote the idea of buying these cards so it fits the theme of the Lucre set. Maybe even don't include the rule wherein you can draw these as defender rewards. But, if you have Incursion, you can shuffle the reward decks together. Even if you don't use Lucre in your game, you can still use the so cards.
So I'm not so much thinking of a special Lucre deck, but rather of a second reward deck disguised as a Lucre deck..