Cheapest priced copy (Commander 2018): $0.49 at Card Kingdom, near mint, their price list as of .
Bloodtracker 
Creature — Vampire Wizard · 2/2 · Rare · Commander 2018 · #14
Flying
{B}, Pay 2 life: Put a +1/+1 counter on this creature.
When this creature leaves the battlefield, draw a card for each +1/+1 counter on it.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
5 printings · $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2018 | 14 | Rare | $0.49 | — |
| Commander 2021 | 137 | Rare | $0.49 | — |
| Jumpstart 2022 | 382 | Rare | $0.49 | — |
| The Lost Caverns of Ixalan Commander | 186 | Rare | $0.49 | — |
| Crimson Vow Commander | 122 | Rare | $0.49 | — |
One ruling from Wizards of the Coast
- 13 July 2018If enough -1/-1 counters are put on Bloodtracker at the same time to make its toughness 0 or less, the number of +1/+1 counters on it before it got any -1/-1 counters will be used to determine how many cards you draw. For example, if there are three +1/+1 counters on Bloodtracker and it gets six -1/-1 counters, you'll draw three cards. That's because Bloodtracker's triggered ability checks the creature's existence just before it leaves the battlefield, and it still has all those counters on it at that point.