Cheapest priced copy (Masters 25): $0.59 at Card Kingdom, near mint, their price list as of .
Sai of the Shinobi 
Artifact — Equipment · Uncommon · Planechase 2012 · #113
Equipped creature gets +1/+1.
Whenever a creature you control enters, you may attach this Equipment to it.
Equip {2}
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
3 printings · $0.59 to $1.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Masters 25 | 230 | Uncommon | $0.59 | $1.99 |
| Planechase 2012 | 113 | Uncommon | $0.79 | — |
| Planechase Anthology | 113 | Uncommon | $0.69 | — |
One ruling from Wizards of the Coast
- 16 March 2018If you choose not to attach Sai of the Shinobi to a creature that enters the battlefield, or if you can't (most likely because the creature has left the battlefield by the time the triggered ability resolves), Sai of the Shinobi doesn't move.