Cheapest priced copy (Guilds of Ravnica): $0.49 at Card Kingdom, near mint, their price list as of .
Blood Operative 
Creature — Vampire Assassin · 3/1 · Rare · Guilds of Ravnica · #63
Lifelink
When this creature enters, you may exile target card from a graveyard.
Whenever you surveil, if this card is in your graveyard, you may pay 3 life. If you do, return this card to your hand.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
2 printings · $0.49 to $0.59 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Guilds of Ravnica | 63 | Rare | $0.49 | $0.49 |
| Guilds of Ravnica Promos | 63s | Rare | — | $0.59 |
3 rulings from Wizards of the Coast
- 5 October 2018If you surveil and put Blood Operative into your graveyard as you do so, its ability triggers once you've finished surveilling.
- 5 October 2018No player may take actions between the time you choose to pay 3 life and the time you return Blood Operative to your hand.
- 12 January 2024An ability that triggers "whenever you surveil" triggers after you're done surveilling, even if you have fewer cards in your library than the number of cards you're instructed to surveil. It even triggers if you have no cards in your library.