Renegade Rallier is generating a lot of Modern buzz, and in its first week of legality already made it to the finals of a Modern Classic! Jermol Jupiter played three copies of the Aether Revolt uncommon in his second place Abzan Company deck this past weekend. The card that is seeing movement, however, is the one-of Time Spiral rare in his list.
Saffi gives the deck another infinite combo by combining with Viscera Seer, Renegade Rallier, and Anafenza, Kin-Tree Spirit. You sacrifice your Saffi targetting your Rallier, then sacrifice your Rallier to your Seer, and then the Rallier comes back and brings the Saffi back with it. All the while, your Anafenza generates bolster triggers.
Saffi currently has a sparse 14 listings on TCGPlayer, with most of them being over $10. A one-of in a Modern deck for a back-door combo doesn't generate a lot of demand, though Time Spiral hasn't been in print for years. This isn't the only combo that Saffi fits into, and it has some Cube/Commander demand as well, though I wouldn't expect Saffi to climb too much higher. I'd be happier as a seller than a buyer at the current price.