Boy, the data looks great on this, so I'll keep it short and sweet.
I'm a bit wary that this will see a Commander reprint, dropping it back down to $1. This is highly reprintable, and Saviors of Kamigawa was a very low print-run. A reprint will hose the value here.
For $2 or less, non-Foil Promise of Bunrei looks good as a short-term spec. They're spiking to $8, then falling to $5.
For $10 or less, Foils are a good short, medium and long-term spec. They're spiking to $15+ and not looking back.