Cheapest priced copy (Mirage): $0.35 at Card Kingdom, near mint, their price list as of .
Sabertooth Cobra 
Creature — Snake · 2/2 · Common · The List · #MIR-238
Whenever this creature deals damage to a player, that player gets a poison counter. The player gets another poison counter at the beginning of their next upkeep unless they pay {2} before that step. (A player with ten or more poison counters loses the game.)
Legal inCommanderLegacyVintagePauper
Not legal inBrawlStandardPioneerModern
2 printings · $0.35 to $0.39 at Card Kingdom
One ruling from Wizards of the Coast
- 4 October 2004The ability still gives a poison counter even if Sabertooth Cobra leaves the battlefield before the next upkeep.