Cheapest priced copy (Magic 2012): $0.35 at Card Kingdom, near mint, their price list as of .
Blood Seeker 
Creature — Vampire Shaman · 1/1 · Common · Duskmourn: House of Horror Commander · #77
Whenever a creature an opponent controls enters, you may have that player lose 1 life.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
3 printings · $0.35 to $3.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Duskmourn: House of Horror Commander | 77 | Common | $0.99 | — |
| Magic 2012 | 81 | Common | $0.35 | $3.49 |
| Zendikar | 80 | Common | $0.35 | $3.99 |
One ruling from Wizards of the Coast
- 22 September 2011Life loss is not the same as damage. Blood Seeker's ability will not cause creatures with bloodthirst to enter with +1/+1 counters.