Cheapest priced copy (Magic 2014): $0.49 at Card Kingdom, near mint, their price list as of .
Sentinel Sliver 
Creature — Sliver · 2/2 · Common · The List · #M14-30
Sliver creatures you control have vigilance. (Attacking doesn't cause them to tap.)
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
3 printings · $0.49 to $10.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Masters | 835 | Common | $5.49 | — |
| Magic 2014 | 30 | Common | $0.49 | $10.99 |
| The List | M14-30 | Common | $0.79 | — |
2 rulings from Wizards of the Coast
- 1 July 2013Abilities that Slivers grant, as well as power/toughness boosts, are cumulative. However, for some abilities, like flying, having more than one instance of the ability doesn’t provide any additional benefit.
- 1 July 2013If you change the creature type of a Sliver you control so it’s no longer a Sliver, it will no longer be affected by its own ability. Its ability will continue to affect other Sliver creatures you control.